Complex sentence: Chartered as a town on March 12,1803, Port Gibson is Mississippi's third-oldest European-American settlement, being occupied in 1729 by French colonists, as it was then within French-claimed territory, "La Louisiane".
Split into simpler sentences: Chartered as a town on March 12,1803, Port Gibson is Mississippi's third-oldest European-American settlement. It was developed beginning in 1729 by French colonists, and was then within French-claimed territory, "La Louisiane".