The 550-foot Washington Monument was the tallest freestanding structure in the world when it was completed in 1884. Electrical knowledge was still primitive at the time, but the designers knew that some kind of lightning protection system was required when building at that height.
Their solution was a solid aluminum pyramidion at the very tip top of the monument. It connected to four wrought iron columns inside the hollow monument that served double duty as supports for the elevator. From there, electricity was supposed to shoot down the Washington Monument 40 feet underground into a small pool of groundwater that would dissipate the charge.
The aluminum pyramidion—at the time, worth its weight in silver—was installed with great fanfare in December 1884. However according to Dru Smith of the National Geodetic Survey (NGS), the system didn’t quite work as promised. “Within the first six months they went back up and found that it had been struck by lightning; they hadn’t even finished taking the scaffolding down. It ended up doing too good of a job and melted down about 3/8ths of an inch," Smith told Atlas Obscura.
Project lead Thomas Lincoln Casey of the Army Corps of Engineers responded by installing a spiked collar for the monument to divert the lightning strikes, rendering the expensive pyramidion useless. The underground lightning-dissipation pool was also taken out of service “almost immediately,” according to the NGS.
The spiked collar remained in use until the 2011 Washington earthquake forced significant repairs to the monument. It came off in 2013 and was replaced by two less obtrusive rods. The useless pyramidion is still in place, though, and the Washington Monument is still constantly being hit by lightning.