There was an old Norse Wall presumably built by Thorwald Ericson (Lief Ericson's brother) and the Vikings in about 1,000 A.D.   The wall was discovered in about 1823 during construction and a piece currently resides in the Provincetown Museum.  Unfortunately, the site was covered up leaving the wall about 25 feet below the surface in 1853 and an inn sits on the site now known as the Norse Wall Inn.

Jack Crane

Cape Cod's Provincetown Harbor

Provincetown Harbor is a large natural harbor located in the town of Provincetown, Massachusetts. The harbor is mostly 30 to 90 feet (9 to 27 m) deep and stretches roughly 1 mile (1.6 km) from northwest to southeast and 2 miles (3.2 km) from northeast to southwest – one large, deep basin with no dredged channel necessary for boats to enter and exit.

• http://en.wikipedia.org/wiki/Provincetown Harbor
• http://www.capelinks.com/cape-cod/main/entry/the-norse-wall/