The Back Bay Fens, called simply The Fens most commonly, is a parkland and urban wild in Boston. The Fens park is essentially an ancient spot of saltwater marshland which has been surrounded by dry land, disconnected from the tides of the Atlantic Ocean, and landscaped into a park with fresh water within. When Boston was settled in the early 1600s the Shawmut Peninsula on which it was built was connected to Roxbury by a spit of sandy ground called "The Neck." The adjacent area of marshland to the west was a tidal flat of the Charles River. The area became malodorous with time as it became tainted with sewage from the growing settlement.