Here’s a drawing we found from the Library of Congress depicting the finishing touches on the Washington Monument – the placement of the capstone.
This capstone, made of aluminum, was placed atop the monument in 1885, 37 years after construction on the monument began. See images of its halted construction here. The capstone has gotten a lot of attention for the inscription on its East facing side, which says Laus Deo, meaning “Praise be to God”. The capstone also got attention in Dan Brown’s book The Lost Symbol.
Source: Library of Congress