the gateway arch is a great engineering achievement. from being built both legs at the same time with cranes walking up the sides of the legs to the unique one-of-a-kind elevator system that it uses. when the final wedge went into the arch to complete it they had something like 1 inch of play or the whole thing would have collapsed.
the whole thing is neat. if anyone is by st louis with time to kill i suggest going in the arch. and go through the musuem thing where it shows how it was built. its very interesting.