Washington Monument

History

The monument was built to honor George Washington, the first president of the United States. At Washington's death in 1799, he was the unchallenged public icon of U.S. military and civic patriotism. He was also identified with the Federalist Party, which lost control of the national government in 1800 to the Jeffersonian Republicans, who were reluctant to celebrate the hero of the opposition party.

Proposals

After the American Revolutionary War, there were many proposals to build a monument to Washington, beginning with an authorization in 1783 by the old Confederation Congress to erect an equestrian statue of the general in a future U.S. national capital city. The initial proposal called for an equestrian statue.

On December 24, 1799, ten days after Washington's death, a U.S. congressional committee recommended a different type of monument. U.S. representative John Marshall proposed that a tomb be erected within the Capitol, but a lack of funds, disagreement over what type of memorial to build, and the Washington family's reluctance to move his body from Mount Vernon prevented progress on any project. The Democratic-Republican Party (Jeffersonian Republicans) took control of Congress in 1801 and rescinded prior approvals for the memorial. Further political squabbling, along with the American Civil War, blocked the completion of the Washington Monument for much of the 19th century.

Design

Progress toward a memorial finally began in 1833, when a group of citizens formed the Washington National Monument Society. On September 23, 1835, the board of managers of the society described their expectations:It is proposed that the contemplated monument shall be like him in whose honor it is to be constructed, unparalleled in the world, and commensurate with the gratitude, liberality, and patriotism of the people by whom it is to be erected ... [It] should blend stupendousness with elegance, and be of such magnitude and beauty as to be an object of pride to the American people, and of admiration to all who see it. Its material is intended to be wholly American, and to be of marble and granite brought from each state, that each state may participate in the glory of contributing material as well as in funds to its construction.

In 1836, after they had raised $28,000 in donations (equivalent to $1,000,000 in 2024), they announced a competition for the design of the memorial. Robert Mills was formally selected in 1845. Mills had previously designed a monument to George Washington in nearby Baltimore in 1815, and he had just been chosen Architect of Public Buildings for Washington. His design called for a circular colonnaded building 250 feet (76 m) in diameter and 100 feet (30 m) high, supporting a four-sided obelisk 500 feet (150 m) high, for a total height of 600 feet (180 m). A massive cylindrical pillar 70 feet (21 m) in diameter would support the obelisk at the center of the building. The obelisk was to be 70 feet (21 m) square at the base and 40 feet (12 m) square at the top with a slightly peaked roof. Both the obelisk and pillar were hollow within which a railway spiraled up. The obelisk had no doorway—instead its interior was entered from the interior of the pillar upon which it was mounted. The pillar had an "arched way" at its base. The top of the portico of the building would feature Washington standing in a chariot holding the reins of six horses. Inside the colonnade would be statues of 30 prominent Revolutionary War heroes and statues of the 56 signers of the Declaration of Independence.

Criticism of Mills's design came up already in 1847, when architect Henry Robinson Searle from Rochester presented an alternative concept, backed by three objections against Mills's project:

First, would the foundation sustain the weight of the required height, and especially with the increased localized pressure in a storm of wind; second, the mere obelisk appeared only as an enlarged plagiarism, in no way illustrating the memory of Washington personally, or those connected with him, or the history of this growing country; third, there is nothing whatever aesthetic about it, and nothing that would impress the visitor, whether native or foreign, with the grandeur of the work of Washington and his coadjutors in founding this nation.

Construction

The Washington Monument was originally intended to be located at the intersection of a north–south axis through the center of the White House, and a west–east axis through the U.S. Capitol on Capitol Hill. This site had been allocated as part of the 1791 L'Enfant Plan for Washington, D.C. The ground at the intended location proved to be too unstable to support such a heavy structure, so the monument's location was moved 390 feet (118.9 m) east-southeast. At that originally intended site there now stands a small monolith called the Jefferson Pier. Consequently, the McMillan Plan specified that the Lincoln Memorial should be "placed on the main axis of the Capitol and the Monument", about 1° south of due west of the Capitol or the monument, not due west of the Capitol or the monument.

The cornerstone was laid with great ceremony on July 4, 1848. The ceremony began with a parade of dignitaries in carriages, marching troops, fire companies, and benevolent societies. A long oration was delivered by Robert C. Winthrop, the speaker of the House of Representatives. Subsequently, workers excavated the site, laid the cornerstone on the prepared bed, and laid the original foundation around and on top of the cornerstone. Construction of its massive walls began in 1849. Regarding modern claims of slave labor being used in construction, Washington Monument historian John Steele Gordon stated "I can't say for certain, but the stonemasonry was pretty highly skilled, so it's unlikely that slaves would've been doing it. The stones were cut by stonecutters, which is highly skilled work; and the stones were hoisted by means of steam engines, so you'd need a skilled engineer and foreman for stuff like that. Tending the steam engine, building the cast-iron staircase inside—that wasn't grunt work. ... The early quarries were in Maryland, so slave labor was undoubtedly used to quarry and haul the stone". Abraham Riesman, who quoted Gordon, states "there were plenty of people who worked as skilled laborers while enslaved in antebellum America. Indeed, there were enslaved people who worked as stonemasons. So the possibility remains that there were slaves who performed some of the necessary skilled labor for the monument." According to historian Jesse Holland, it is very likely that African American slaves were among the construction workers, given that slavery prevailed in Washington and its surrounding states at that time, and slaves were commonly used in public and private construction.

During the second phase, it is unlikely that slave labor was used, as every stone laid required dressing and polishing by a skilled stonemason. This includes the iron staircase which was constructed 1885–86. That the stonecutters in the quarry were slaves is confirmed because all quarry workers were slaves during the construction of the United States Capitol during the 1790s. However, most of the first phase's construction only required unskilled manual labor. No information survives concerning the method used to lift stones that weighed several tons each during the first phase, whether by a manual winch or a steam engine. The surviving information concerning slaves that built the core of the United States Capitol during the 1790s is not much help. At the time, the District of Columbia outside of Georgetown was sparsely populated so the federal government rented slaves from their owners who were paid a fee for their slaves' normal daily labor. Any overtime for Sundays, holidays, and nights was paid directly to the slaves which they could use for daily needs or to save to buy their freedom. Conversely, the first phase of the monument was constructed by a private entity, the Washington National Monument Society.

Dedication

The monument was dedicated on February 21, 1885. Over 800 people were present on the monument grounds to hear speeches by Ohio senator John Sherman, the Rev. Henderson Suter, William Wilson Corcoran of the Washington National Monument Society (read by James C. Welling), Freemason Myron M. Parker, Col. Thomas Lincoln Casey of the Army Corps of Engineers, and President Chester A. Arthur. President Arthur proclaimed: I do now ... in behalf of the people, receive this monument ... and declare it dedicated from this time forth to the immortal name and memory of George Washington.

After the speeches, Lieutenant-General Philip Sheridan led a procession past the White House, via Pennsylvania Avenue to the east main entrance of the Capitol Building, where U.S. representative John Davis Long read a speech written a few months earlier by Robert C. Winthrop. A final speech was given by U.S. senator John W. Daniel. The festivities concluded that evening with fireworks, both aerial and ground displays. The total cost of the monument from 1848 to 1888 was $1,409,500 (equivalent to $40,000,000 in 2024).

Later history

The Washington Monument was the world's tallest structure until the Eiffel Tower in Paris was completed in 1889. This monument is taller than the obelisks around the capitals of Europe and in Egypt and Ethiopia, but ordinary antique obelisks were quarried as a monolithic block of stone, and were therefore seldom taller than approximately 100 feet (30 m). The district's Heights of Buildings Act of 1910 restricts new building heights to no more than 20 feet (6.1 m) greater than the width of the adjacent street; as such, none of Washington, D.C.'s tallest buildings are higher than the Washington Monument.

In the early 1900s, material started oozing out between the outer stones of the first construction period below the 150-foot (46 m) mark, and was referred to by tourists as "geological tuberculosis". This was caused by the weathering of the cement and rubble filler between the outer and inner walls. As the lower section of the monument was exposed to cold and hot and damp and dry weather conditions, the material dissolved and worked its way through the cracks between the stones of the outer wall, solidifying as it dripped down their outer surface.

For ten hours in December 1982, the Washington Monument and eight tourists were held hostage by a nuclear arms protester, Norman Mayer, claiming to have explosives in a van he drove to the monument's base. United States Park Police shot and killed Mayer. The monument was undamaged in the incident, and it was discovered later that Mayer did not have explosives. After this incident, the surrounding grounds were modified in places to restrict the possible unauthorized approach of motor vehicles.

The monument underwent an extensive restoration project between 1998 and 2001. During this time it was completely covered in scaffolding designed by Michael Graves (who was also responsible for the interior changes). The project included cleaning, repairing and repointing the monument's exterior and interior stonework; adding glass encasements around stone in publicly accessible interior spaces to prevent vandalism; and adding windows with narrower frames to increase the viewing space. New exhibits celebrating the life of George Washington, and the monument's place in history, were also added.

A temporary interactive visitor center, dubbed the "Discovery Channel Center", was also constructed during the project. The center provided a simulated ride to the top of the monument, and shared information with visitors during phases in which the monument was closed. The majority of the project's phases were completed by summer 2000, allowing the monument to reopen July 31, 2000. The monument temporarily closed again on December 4, 2000, to allow a new elevator cab to be installed, completing the final phase of the restoration project. The new cab included glass windows, allowing visitors to see some of the 194 memorial stones with their inscriptions embedded in the monument's walls. The installation of the cab took much longer than anticipated, and the monument did not reopen until February 22, 2002. The final cost of the restoration project was $10.5 million.

Components

Foundation

The first phase began with the excavation of about 7 feet 8 inches (2.3 m) of topsoil down to a level of loam, consisting of equal parts of sand and clay, hard enough to require picks to break it up. On this "bed of the foundation" the cornerstone was laid at the northeast corner of the proposed foundation. The rest of the foundation was then constructed of bluestone gneiss rubble and spalls, with every crevice filled with lime mortar. The dimensions of this old foundation were 23 feet 4 inches (7.1 m) high, 80 feet (24.4 m) square at the base, and 58 feet 6 inches (17.8 m) square at the top, laid down in eight steps, similar to a truncated step pyramid. At the center of the foundation a brick-lined 2-foot (60 cm) square well was dug to a depth of 20 feet (6 m) below the bed of the foundation to keep it dry and to supply water during construction.

During the second phase, after determining that the proposed weight of the monument was too great for the old foundation to safely bear, the thickness of the walls atop the unfinished stump was reduced and the foundation was strengthened by adding a large unreinforced concrete slab below the perimeter of the old foundation to increase the monument's load bearing area two and one half times. The slab was 13 feet 6 inches (4.1 m) thick, with an outer perimeter 126 feet 5+1⁄2 inches (38.54 m) square, an inner perimeter 44 feet (13.4 m) square, with undisturbed loam inside the inner perimeter except for the water well. The area at the base of the second phase foundation is 15,992 square feet (1,485.7 m2). The strengthened foundation (old foundation and concrete slab) has a total depth of 36 feet 10 inches (11.2 m) below the bottom of the lowest course of marble blocks (now below ground), and 38 feet (11.6 m) below the entry lobby floor. Casey reported that nowhere did the load exceed 9 long tons per square foot (140 psi; 970 kPa) and did not exceed 3 long tons per square foot (47 psi; 320 kPa) near the outer perimeter. To properly distribute the load from the shaft to slab, about half by volume of the outer periphery of the old rubble foundation below its top step was removed. A continuous sloping unreinforced concrete buttress encircles what remains. The buttress is 100 feet 4 inches (30.6 m) square at its base, 64 feet 6 inches (19.7 m) square at its top, and 20 feet 5 inches (6.2 m) high. The perimeter of the original top step of the old rubble foundation rests on the larger top of the concrete buttress. Its slope (lower external angle from the vertical) is 49°. This buttress rests in a depression (triangular cross-section) on the top surface of the concrete slab. The slab was constructed by digging pairs of 4-foot (1.2 m) wide drifts on opposite sides of the monument's center line to keep the monument properly balanced. The drifts were filled with unreinforced concrete with depressions or dowel stones on their sides to interlock the sections. The weight of the foundation is 36,912 long tons (41,341 short tons; 37,504 tonnes).

Cornerstone

The cornerstone was laid at the northeast corner of the lowest course of the old foundation on July 4, 1848. Therefore, the cornerstone was laid below the 1848 ground level. In 1880, the ground level was raised 17 feet (5.2 m). If the cornerstone had not been moved during the strengthening of the foundation in 1879–80, its upper surface would now be 21 feet (6.4 m) below the pavement just outside the northeast corner of the shaft. It would now be sandwiched between the concrete slab under the old foundation and the concrete buttress completely encircling what remains of the old foundation. During the strengthening process, about half by volume of the periphery of the lowest seven of eight courses or steps of the old foundation (gneiss rubble) was removed to provide good footing for the buttress. Although a few diagrams, pictures and descriptions of this process exist, the fate of the cornerstone is not mentioned.

The cornerstone was a 24,500-pound (11,100 kg) marble block 2.5 feet (0.76 m) high and 6.5 feet (2.0 m) square with a large hole for a zinc case filled with memorabilia. The hole was covered by a copper plate inscribed with the date of the Declaration of Independence (July 4, 1776), the date the cornerstone was laid (July 4, 1848), and the names of the managers of the Washington National Monument Society. The memorabilia in the zinc case included items associated with the monument, the city of Washington, the national government, state governments, benevolent societies, and George Washington, plus miscellaneous publications, both governmental and commercial, a coin set, and a Bible, totaling 73 items or collections of items, as well as 71 newspapers containing articles relating to George Washington or the monument.

Memorial stones

States, cities, foreign countries, benevolent societies, other organizations, and individuals have contributed 194 memorial stones, all inserted into the east and west interior walls above stair landings or levels for easy viewing, except one on the south interior wall between stairs that is difficult to view. The sources disagree on the number of stones for two reasons: whether one or both "height stones" are included, and stones not yet on display at the time of a source's publication cannot be included. The "height stones" refer to two stones that indicate height: during the first phase of construction a stone with an inscription that includes the phrase "from the foundation to this height 100 feet" (30 m) was installed just below the 80–90-foot (24–27 m) stairway and high above the 60–70-foot (18–21 m) stairway; during the second phase of construction a stone with a horizontal line and the phrase "top of statue on Capitol" was installed on the 330-foot (100 m) level.

The Historic Structure Report (HSR, 2004) named 194 "memorial stones" by level, including both height stones. Jacob (2005) described in detail and pictured 193 "commemorative stones", including the 100 foot (30 m) stone but not the Capitol stone. The Historic American Buildings Survey (HABS, 1994) showed the location of 193 "memorial stones" but did not describe or name any. HABS showed both height stones but did not show one stone not yet installed in 1994. Olszewski (1971) named 190 "memorial stones" by level, including the Capitol stone but not the 100-foot stone. Olszewski did not include three stones not yet installed in 1971.

Of 194 stones, 94 are marble, 40 are granite, 29 are limestone, 8 are sandstone, with 23 miscellaneous types, including stones with two types of material and those whose materials are not identified. Unusual materials include native copper (Michigan), pipestone (Minnesota), petrified wood (Arizona), and jadeite (Alaska). The stones vary in size from about 1.5 feet (0.46 m) square (Carthage) to about 6 by 8 feet (1.8 m × 2.4 m) (Philadelphia and New York City).

Utah contributed one stone as a territory and another as a state, both with inscriptions that include its pre-territorial name, Deseret, both located on the 220-foot (67 m) level.

A stone at the 240-foot (73 m) level of the monument is inscribed in Welsh: Fy Iaith, Fy Ngwlad, Fy Nghenedl, Cymry am byth (My Language, My Country, My Nation, Welsh forever). The stone, imported from Wales, was donated by Welsh citizens of New York. Two other stones were presented by the Sunday Schools of the Methodist Episcopal Church in New York and the Sabbath School children of the Methodist Episcopal Church in Philadelphia—the former quotes from the Bible verse Proverbs 10:7, "The memory of the just is blessed".

Walls

The bottom section of 152 feet (46 m) was built between 1848 and 1854 under the direction of William Dougherty. It uses white Cockeysville Marble from the Texas Quarry, a still-active quarry in Cockeysville, Maryland. During the second phase in 1879–1880, eight feet of white marble from Sheffield, Massachusetts, were laid above the "Texas" marble; this was halted due to quality control problems. The third and final phase of 390 feet (120 m) is marble from the Beaver Dam quarry adjacent to the Texas quarry (1880–1884). The marble here was a warmer shade than the starker white of the Texas quarry. The three different shades of marble can be distinguished on the monument. Engineers used three different systems to measure the monument's levels. The height of the marble walls was measured in 2-foot (0.61 m) increments, the pyramid-shaped top was measured in 4-foot (1.2 m) increments, and the stair landings were marked in 10-foot (3.0 m) increments. Complicating matters, the starting "zero point" for the staircase was different from the one used for the walls, and these references even shifted slightly when construction resumed for the second phase.

Since there was a long hiatus between the first phase and the last two phases, the monument has a complex superstructure. Around the 150-foot (46 m) level, the inner walls slope slightly outward, causing the hollow shaft inside to widen from about 25 feet (7.6 m) square to over 31 feet (9.4 m) square. Above this level, the monument's upper section has thinner walls. The lowest part of the upper section has walls measuring 8 feet (2.4 m) thick, which featured distinctively rounded corners; these walls gradually tapered to one and a half feet (0.46 m) thick at the top. The weight of this upper portion alone is 21,260 long tons (21,600 t). In total, the monument's interior walls rise to a height of just over 500 feet (150 m).

During the first phase of construction, the monument's walls were built with a less refined technique. While the outer surface is made of thick marble stones arranged in 2-foot-high (0.61 m) rows, the core of the walls was filled with a random assortment of bluestone rubble, all held together by mortar. At its base, this first section is 55 feet (17 m) square with massive 15-foot-thick (4.6 m) walls, and this lower portion alone weighs nearly 22,400 long tons (22,800 t). During the second phase, engineers used precisely cut blocks of marble and granite laid in an orderly, interlocking pattern with thick, stable joints. For strength, the marble exterior was initially backed-filled by granite blocks. As the monument rose, the builders gradually transitioned to using marble for the interior as well, until the structure above the 450-foot (140 m) level was made entirely of solid marble blocks.

Pinnacle

The pyramidion, atop the monument, has a marble capstone shaped like a truncated pyramid, with a cubical keystone projecting from its base and a deep groove surrounding the keystone. The aluminum apex replaces its truncated top. The inside upper edges of the topmost slabs on the four faces of the pyramidion rest on the keystone and in the groove. It has a large vertical hole through which a 1.5-inch (3.8 cm) threaded copper rod passes and screws into the base of the apex, which used to form part of its lightning protection system. The keystone and groove occupy so much of its base that only a small horizontal area near its outer edge remains. The weight of the capstone is transferred to both the inner and outer portions of the shiplap upper edges of the slabs. It weighs 3,300 pounds (1,500 kg), is 5 feet 2 inches (1.57 m) high from its base to its top, and is 3 feet (91 cm) square at its base.

The marble pyramidion has an extremely complex construction to save weight yet remain strong. Its surface slabs or panels are usually only 7 inches (18 cm) thick (with small thick and thin portions) and generally do not support the weight of slabs above them, instead transferring their own weight via 1-foot (30 cm) wide internal marble ribs to the shaft's walls. The slabs are generally 7 feet (2 m) wide and 4 feet 4 inches (1 m) high with a 2-inch (5 cm) vertical overlap (shiplap) to prevent water from entering the horizontal joints. Twelve such courses, the internal ribs, the marble capstone, and the aluminum apex comprise the pyramidion. Its height is 55 feet 0 inches (16.76 m). Its weight is 300 long tons (336 short tons; 305 tonnes). The slope of the walls of the pyramidion is 17°24' from the vertical. There are twelve ribs, three per wall, which spring from the 470-foot (143.3 m) level, all being integrated into the walls up to the 500-foot (152.4 m) level. All are free standing above 500 feet, relying on mortise and tenon joints to attach neighboring stones. The eight corner ribs terminate six courses above the shaft, each corner rib resting on its neighboring corner rib via a miter joint, forming four corner arches. Each such arch supports a pair of square corner stones, one above the other totaling one course in height. Each corner rib is linked to the nearest center rib at the sixth course via a marble tie beam. The four center ribs terminate eight courses above the shaft at a marble cruciform (cross shaped) keystone, forming two main arches that cross each other. Two stones, each one-course high, are mounted on each of the four ribs, supporting two additional courses above the cruciform keystone, leaving two courses to support the capstone's weight by themselves.

The observation floor (nominally the 500-foot level) is 499 feet 4+1⁄2 inches (152.21 m) above the entry lobby floor or lowest landing level. It is 1+1⁄4 inches (3.2 cm) above the marble base of the pyramidion and the top of the shaft walls.

Stairs and elevator

The monument is filled with ironwork, consisting of its stairs, elevator columns and associated tie beams, none of which supports the weight of the stonework. It was redesigned in 1958 to reduce congestion and improve the flow of visitors. Originally, visitors entered and exited the west side of the elevator on the observation floor, causing congestion. So the large landing at the 490-foot level was expanded to a full floor and the original spiral stair in the northeast corner between the 490-and-500-foot (149.4 and 152.4 m) levels was replaced by two spiral stairs in the northeast and southeast corners. Now visitors exit the elevator on the observation floor, then walk down either spiral stair before reboarding the elevator for their trip back down.

The main stairs spiral up the interior walls from the entry lobby floor to the elevator reboarding floor at the 490-foot (150 m) level. The elevator occupies the center of the shaft well from the entry lobby to the observation floor, with an elevator machine room (installed 1925–26) whose floor is 18 feet 10 inches (5.74 m) above the observation floor and an elevator pit (excavated 1879) whose floor is 9 feet (2.74 m) below the entry lobby floor. The stairs and elevator are supported by four wrought iron columns each. The four supporting the stairs extend from the entry lobby floor to the observation floor and were set at the corners of a 15-foot-8-inch (4.78 m) square. The four supporting the elevator extend from the floor of the elevator pit to 14 feet (4.3 m) above the observation floor and were set at the corners of a 9-foot-9+1⁄2-inch (3.0 m) square. The weight of the ironwork is 275 long tons (308 short tons; 279 tonnes). Cast iron, wrought iron, and steel were all used. The two small spiral stairs installed in 1958 are aluminum.

Most landings occupy the entire east and west interior walls every 10 feet (3.05 m) from and including the east landing at the 30-foot (9.1 m) level up to the west landing at the 480-foot (150 m) level, east then west alternately. Three stairs with small landings rise from the entry lobby floor to the 30-foot (9.1 m) level successively along the north, west and south interior walls. Landings from the 30 foot (9.1 m) level up to the 150 foot (46 m) level are 3 feet 2+1⁄4 inches (0.97 m) by 25 feet 1 inch (7.65 m), while landings from the 160-foot (49 m) level to the 480-foot (150 m) level are 7 feet 10+3⁄4 inches (2.41 m) by 31 feet 5+1⁄2 inches (9.59 m). All stairs are on the north and south walls except for the aforementioned west stair between the 10–20-foot (3.05–6.10 m) levels, and the two spiral stairs.

Height

The monument stands 554 feet 7+11⁄32 inches (169.046 m) tall according to the National Geodetic Survey (measured 2013–14) or 555 feet 5+1⁄8 inches (169.294 m) tall according to the National Park Service (measured 1884). In 1975, a ramp covered two steps at the entrance to the monument, so the ground next to the ramp was raised to match its height, reducing the remaining height to the monument's apex. It is the third tallest monumental column in the world, trailing only the Juche Tower in Pyongyang (560 ft/170 m) and the San Jacinto Monument in Houston, Texas (567.31 ft/172.92 m), though neither of those are all stone nor true obelisks.

The tallest masonry structure in the world is the brick Anaconda Smelter Stack in Montana at 585 feet 1+1⁄2 inches (178.35 m) tall; this includes a 30-foot (9.1 m) non-masonry concrete foundation, leaving the stack's brick chimney at 555 feet 1+1⁄2 inches (169.20 m) tall. If the monument's aluminum apex is also discounted, then the stack's masonry portion is 15 inches (38 cm) taller than the monument's masonry portion.

Miscellaneous details

The weight of the above ground portion of the monument is 44,208 long tons (49,513 short tons; 44,917 tonnes), whereas its total weight, including the foundation below ground and any earth above it that is within its outer perimeter is 81,120 long tons (90,854 short tons; 82,422 tonnes). The total number of blocks in the monument, including all marble, granite and gneiss blocks, whether externally or internally visible or hidden from view within the walls or old foundation is over 36,000.

Grounds

The monument is surrounded by an earthen terrace 60 feet (18 m) wide, with its top at the base of the walls and steeply sloped sides. This was constructed in 1880–81 over the reinforced foundation. During 1887–88, a knoll was constructed around the terrace tapering out roughly 300 feet (90 m) onto the surrounding terrain. This earthen terrace and knoll buttress the foundation.

Flags

Fifty U.S. national flags, one representing each state, are flown 24 hours a day around a large circle centered on the monument. Forty-eight American flags (one for each state then in existence) were flown on wooden flag poles on Washington's birthday since 1920 and later on Independence Day, Memorial Day, and other special occasions until early 1958. Both the flags and flag poles were removed and stored between these days. In 1958 fifty 25-foot (7.6 m) tall aluminum flag poles (anticipating Alaska and Hawaii) were installed, evenly spaced around a 260-foot (79 m) diameter circle. During 2004–05, the diameter of the circle was reduced to 240 feet (73 m). Since Washington's birthday in 1958, 48 U.S. flags were flown on a daily basis, increasing to 49 flags on July 4, 1959, and then to 50 flags since July 4, 1960. When fewer than 50 flags were flown, only the flag poles in use were placed into base receptacles, and all flags were removed and stored overnight. Since July 4, 1971, fifty U.S. flags have flown 24 hours a day.

Visitation

The Washington Monument attracted enormous crowds before it officially opened. For six months after its dedication, 10,041 people climbed the stairs to the top. After the elevator that had been used to raise building materials was altered to carry passengers, the number of visitors grew rapidly, and an average of 55,000 people per month were going to the top by 1888, only three years after its completion and dedication. The annual visitor count peaked at an average of 1.1 million people between 1979 and 1997. From 2005 to 2010, when restrictions were placed on the number of visitors allowed per day, the Washington Monument had an annual average of 631,000 visitors. The national memorial was listed on the National Register of Historic Places on October 15, 1966, as with all historic areas administered by the National Park Service (an agency of the U.S. Department of the Interior) at the time.

Security

In 2001, a temporary visitor security screening center – a one-story cube of wood around a metal frame – was added to the east entrance of the Washington Monument in the wake of the September 11 attacks. Visitors passed through metal detectors and bomb-sniffing sensors prior to entering the monument.

In 2019 a new 785-square-foot (72.9 m2) two-story screening facility opened. Its exterior walls are slightly frosted, consisting of an outer sheet of bulletproof glass or polycarbonate, a metal mesh insert, and another sheet of bulletproof glass. The inner sheet consists of two sheets of laminated glass; a 0.5-inch (1.3 cm) airspace between the inner and outer glass walls provides thermal insultion. Geothermal heat pumps on the north side of the monument heat and cool the facility. The new facility also incorporates a staff office. The structure is designed such that it can be removed without damage to the monument.

A recessed trench wall known as a ha-ha has been built to minimize the visual impact of a security barrier surrounding the monument. After the September 11 attacks and another unrelated threat at the monument, authorities had put up a circle of temporary Jersey barriers to block the approach of vehicles. This barrier was replaced by a low 30-inch (76 cm) granite stone wall that doubles as a bench and also incorporates lighting. Designed by the famed landscape architect Laurie Olin, the installation received the 2005 Park/Landscape Award of Merit from the American Society of Landscape Architects.

Replicas

In Ridgeland, Mississippi, off Interstate 55 at the corner of Colony Park Boulevard and Highland Colony Parkway, is a 190-foot (58 m) tall cellphone tower in the shape of the Washington Monument. Other replicas or close resemblances include those at the Jefferson Davis State Historic Site in Fairview, Kentucky, at 351 feet (107 m); Olalla, Washington, at 55 feet (17 m); and another in an office park in Alexandria, Virginia, at 30 feet (9.1 m). A 12-foot (3.7 m) high model is under a manhole near the Washington Monument and serves as a geodetic marker in a national geodetic control network.