The main island on which the town sits is the largest of several at the mouth of the Piscataqua River and was originally called Great Island. Settled in 1623, an earthwork defense was built on Fort Point which would evolve into Fort William and Mary (rebuilt in 1808 as Fort Constitution). Chartered in 1679 as a parish of Portsmouth, it was incorporated on May 30, 1693, and was named "New Castle" after the fort. Until 1719 it included Rye, then called "Sandy Beach", which was set off as a parish. The principal industries were trade, tavern-keeping and fishing. There was also agriculture, using the abundant seaweed as fertilizer.