Complex sentence: By the end of the decade a French encampment called "Port Bayou St. Jean" was near the head of the Bayou, and a small fort "St. Jean" was established at the mouth of the Bayou in 1701.
Split into simpler sentences: By the end of the decade, the French made an encampment called "Port Bayou St. Jean" near the head of the Bayou. They built a small fort "St. Jean" at the mouth of the Bayou in 1701.