This paper studies how the expansion of segregated neighborhoods eroded black wealth in prewar American cities. Using a novel sample of matched addresses, we find that over a single decade rental prices soared by roughly 50% on city blocks that transitioned from all white to majority black. Meanwhile, pioneering black families paid a 28% premium to buy a home on a majority white block, after which their homes lost 10% of their value. These findings strongly suggest that segregated housing markets cost black families much of the gains associated with moving north during the Great Migration.