Fort St. Louis was founded by the French explorer René Robert Cavelier Sieur de La Salle in 1685. The French had come to the middle Texas coast quite by accident. The colonists had intended to settle at the mouth of the Mississippi but miscalculated and landed nearly 400 miles to the west at Matagorda Bay.
La Salle led several small, unsuccessful search parties in repeated attempts to locate the Mississippi and was finally assassinated in the spring of 1687 by one of his own disgruntled men. Twenty remaining colonists at Fort St. Louis survived until late 1688 or early 1689 when the Karankawa attacked and killed all but a few children who they took captive. When a Spanish expedition arrived in April, 1689, they found a fort in shambles and the remains of three of the French settlers. They burned what remained of Fort Saint Louis in an attempt to eradicate all traces of the French presence.
The Spanish soldiers also buried the eight French cannons they found, intending to come back for them later. The Spanish never retrieved the cannons and the site of the fort remained a mystery until a rancher with a metal detector discovered them in the 1990's. Today, seven of the eight cannons can be seen at the Museum of the Coastal Bend in Victoria.
More information on Fort St. Louis.