The Monument is an engineering marvel. The Washington Post recently pointed out an interesting fact in an on-going debate about the Monument as the world's tallest free-standing masonry structure. The Monument's marble blocks are held together by just gravity and friction, and no mortar was used in the process.

The Washington Monument is a marvel of 19th-century engineering, standing 555 feet tall and held together primarily by gravity and friction rather than traditional mortar. While some very thin layers of mortar were used in certain sections to ensure the stones were level, the structural integrity of the obelisk relies on the massive weight of the interlocking marble and granite blocks pressing downward. The base walls are 15 feet thick, tapering to just 18 inches at the top, which creates a low center of gravity. Each block was precisely cut and "dry-fitted" to ensure maximum surface contact, allowing the sheer mass of the structure to resist wind and seismic activity. The 100-ounce aluminum capstone, placed in 1884, acts as the final "anchor" for the pressure. This "dry masonry" technique was a deliberate choice by the U.S. Army Corps of Engineers to ensure the monument's longevity, as mortar can crumble and wash away over centuries, whereas a gravity-bound structure remains stable as long as the foundation—which was heavily reinforced in the 1880s—remains solid.