Eiffel was a French engineer who designed the Eiffel Tower as the entrance arch for the for the 1889 Paris Exhibition. Though it was supposed to be dismantled after the fair, the tower became a landmark and is today the world’s most visited paid monument. Prior to this massive undertaking, Eiffel established his reputation by constructing a series of ambitious railway bridges, including the span across the Douro at Oporto, Portugal. In 1881, he designed the internal framework for what structure? Discuss