Washington Monument - aluminum capstone

When completed in 1884 the Washington Monument was capped with a pyramidion made of cast aluminum, which was then a rare and valuable metal and among the largest aluminum castings of its time. The aluminum capstone doubled as a lightning conductor and marked technological advances in metal production in the late 19th century. The obelisk stands approximately 555 feet tall and the capstone remains a noted feature of the monument's construction history.