The Washington Monument was constructed in two phases after laying the cornerstone in 1848. The color line shows where construction halted in 1856, when private donations to fund the Monument dried up.

The Washington Monument has a distinct "two-toned" appearance because its construction was interrupted for over 20 years. The bottom third of the monument was built between 1848 and 1854 using marble from a quarry in Texas, Maryland. However, construction was halted in 1854 due to a lack of funds and the onset of the American Civil War. When work finally resumed in 1879, the original quarry was no longer available, and the builders had to source marble from different locations, including other quarries in Maryland and Massachusetts. Although the new stones looked similar to the original ones when they were first installed, the different mineral compositions caused the two types of marble to weather and age differently over the last 140 years. This created the "color line" you see today at approximately the 150-foot mark. This visible seam serves as a permanent architectural reminder of the political and financial struggles that nearly prevented the monument from being completed, eventually opening in 1888 as the tallest structure in the world at the time.