In 1632, a fortification was constructed on Fort Hill to defend the town. In 1634, Boston sought defenses farther out in the harbor, on one of the numerous islands which protected the port. In July 1634, the town decided to build a fortification on Castle Island. Deputy Governor Roger Ludlow and Captain John Mason of Dorchester supervised construction of the fort. After a structure was built on the northeast side of the island, the General Court resolved that the fort at Castle Island should be completed before any other fortification was begun. The fort was later known as Castle William and required incoming ships to recognize the fortification and would fire at them if they didn't offer recognition by raising their flag. By the end of the century, the fort had been expanded to create a crossfire with the fort on Governor's Island.