7. Marble Hill
Marble Hill was once the northern tip of of Manhattan, but the Army Corps of Engineers saw that it would be faster for ships to round the island if they didn’t have to go around. So they simply sliced off the outcropping, rendering it an island, and later filled the old river making it part of the Bronx. It leads to some funny jurisdictional things–it’s still technically part of the borough of Manhattan but it has a Bronx zip code and area code!