[bsimpson]

Wall St was an actual (medieval) wall until the turn of the 18th century. It's at the very south of Manhattan, a ten minute walk from the tip of the city it was built to protect.

NYC's postal names are a mess: Manhattanites can write "Manhattan" or "New York". Brooklynites are supposed to write "Brooklyn." Queens denizens write the historic names of the farm towns that used to be there. "Astoria" is actually part of New York City, even though seeing a letter addressed there might make you think it's a town upstate.

The postal service is older than the current boundaries of New York, and they never updated the mail routing to reflect the unified city.

Before the bridges were built, much of what's now NYC was very rural.

[Freedom2]

I believe the medieval era ended in the 15th century, but the wall was built in the 17th. So actually the wall would have actually been a colonial era wall, if going by eras - not to mention the construction style was actually more reminiscent of colonial era structures rather than medieval.