These mounds are the timeworn remains of a fort designed to protect the village of Kaskaskia, a town founded in 1703 as the southern anchor of France's colony in the Illinois Country. During the 1730s, French officials planned to replace the ruined Fort de Chartres near Prairie du Rocher with a stone fortification at this site, but construction ceased when it was determined to be too expensive. By the 1750s, fear of British invasion led French officials to plan again for a major post on the Mississippi; they built a new, massive Fort de Chartres and intended a smaller post here. Construction of an earthen fort began about 1759, but it was never completed. This unfinished fort played no role in the French and Indian War, which ended with the transfer of the Illinois Country from France to Great Britain. A British officer visiting in 1766 found two dilapidated buildings, collapsed wooden gun platforms, and earthworks overgrown with bushes. Kaskaskia passed to the new United States with the Treaty of Paris of 1783, which ended the Revolutionary War. In the 1780s, local bandit John Dodge made his headquarters in the old fort. The U.S. Army reoccupied the post about 1803 and stationed troops there until 1807, and the old fort was last used by local residents fearing attack by Britain's Indian allies during the War of 1812.