St. Louis architect Paul Hohmann tracks St. Louis architecture, history, and construction at his blog, Vanishing St. Louis.
Hohmann is currently featuring photographs of downtown taken at the time of Arch construction. The images dramatically show the moment in time where downtown, the Arch, and river were cut off from each other.
It's ironic that the disconnect happened at the time the Arch was built. 50 years later, under a new management plan for the Arch, everyone is looking for ways to reconnect the city, the Arch, and the river. A review of these images would be a good place to start.