Complex sentence: It was the last of three forts to built on the same spot, the first constructed in 1665-then called Fort Saint Louis-by captain Jacques de Chambly, to protect New France from Iroquois attacks.
Split into simpler sentences: It was the last of three forts to be built on the same site. The first-then called Fort Saint Louis-was constructed in 1665 by captain Jacques de Chambly, to protect New France from Iroquois attacks.