The colony that was built on the island of Jamestown was built in a triangular shape because of safety reasons.
The triangular shape enabled the people living in the colony to have an advantage in defending themselves in case they were attacked. The triangular shape allows a better and uncharacteristic movements which enable better maneuvering, and also confusion among the enemy lines, so the colony was built in this manner so that it can sustain various attacks and not fall.
