I suspect most New Yorkers already know this, but if you don't and are curious, here are photos of the area that today is home to Battery Park City. According to Wikipedia:
The land in Lower Manhattan upon which it stands was created by land reclamation on the Hudson River using over 3 million cubic yards of soil and rock excavated during the construction of the World Trade Center, the New York City Water Tunnel, and certain other construction projects, as well as from sand dredged from New York Harbor off Staten Island.
That's right, the shape of Manhattan isn't at all natural. We humans found it to be too constrictive so we literally built more land so we could build more buildings.