The Spanish regarded the North American Gulf Coast as their turf in the 17th century, sandwiched as it was between their colonies in Mexico and Florida. They were therefore taken aback to find the ruined remains of the French Fort St Louis on the Texas coast in 1689. The French explorer La Salle had established the fort on a return expedition: he first reached the Gulf of Mexico by navigating to the Mississippi Delta through the centre of the continent in 1682. Fort St Louis came to a grisly end: La Salle was murdered by his men, who then succumbed to disease or Indian attack. But the discovery spurred a burst of Spanish activity, founding a string of missions and forts .By 1700, Fort Mississippi and Fort San Carlos de Austria threatened French sea access to the Mississippi. Spanish progress from the west was slower, facing determined Apache resistance, and was usually preceded by the founding of missions, to Christianize the native population. In 1716 and 1721, separate expeditions into the interior of modern day Texas established a network of forts and missions, while French attempts to colonize the interior foundered at the Arkansas Post.