From Fox News 5 November 2015:
-------------------------------------------------------
Workers upgrading water mains under New York City’s Washington Square Park this week discovered a vault containing a large pile of skeletal remains dating back approximately 200 years. ...The land where the park is now located was a so-called potter’s field, or public burial ground, between 1797 and 1825. The city bought the land the following year and turned it into a military parade ground, and then a park.

Historians have estimated that approximately 20,000 people were buried underneath the park.
-------------------------------------------------------

article