18th Century New York City

Archaeologists have identified a leftover wall buried 10 feet beneath Battery Park in New York City, that was built in the mid-1700s. The wall was part of one of the forts that ultimately gave 'Battery Park' its name. Several versions are floating around the Internet today, but this one from the NYT appears the most meaty:
Found: Old Wall in New York, and It's Blocking the Subway

The streets of today's modern cities often hide bits of our ancient (and in this case, not so ancient) past. Here's how ancient cities become buried.