Why do you think the pilgrims built a fort?

To protect against native Indians and big game from attacking, Altho alot of the native Indians were peaceful, there were a number of tribes that were aggressive. Back in the 1600's when north America was being colonised it had a massive population of native Americans(millions) and alot more big native game which were wiped out through recreational hunting, territorial protection, warfare and conquest , using both traditional and biological techiques