As this was happening, Charlesfort fell into despair. A lack of supplies threatened the colonists' lives, most of whom followed René Laudonnière further south into Spanish territory to establish Fort Caroline at the mouth of the St. Johns River. The fort had early success, but the colonists had trouble feeding themselves after turmoil developed with the local Native American tribes. Some colonists sailed home while others deserted and became pirates. Following his release from prison, Ribault was dispatched by the French government to save the settlement. He arrived back at the mouth of the St. Johns River in mid-August with a strong relief expedition of some 600 French soldiers and settlers, including Jacques Le Moyne de Morgues (circa 1533-1588), who had been sent by Charles IX to act as official cartographer and artist on the expedition. On his return to Europe he published an account of the expedition in Frankfurt in 1591, entitled "Brevis narratio eorum quae in Florida Americae provincia Gallis acciderunt" - it shows 42 maps, depicts the inhabitants of Florida and describes their customs. It is regarded as an important archive of life in that period.
The same hurricane that masked the approach of Menéndez's troops on Fort Caroline, utterly destroyed all of Ribault’s fleet, driving them up on the beach many miles south of their intended target. Several hundred soldiers and sailors made it ashore barely alive and then walked from near present-day Daytona Beach to Matanzas Inlet, 14 miles south of St. Augustine. The marooned sailors were soon tracked down by Menéndez and a patrol force of Spanish troops, probably under a hundred men. Ribault, believing his hungry men would be fed and decently treated, allowed himself to be bluffed into surrender. In batches of ten, the Frenchmen were rowed across to the mainland, hands tied behind their backs. Following the explicit orders of King Phillip II of Spain, the prisoners were asked if they were professing Catholics. Those who were not were marched behind a dune and put to the knife by Menéndez's Spanish soldiers. Only a handful of Catholics, young musicians and ship's boys were spared their lives. A similar surrender and mass execution of a smaller group of Frenchmen followed a few days later. This time, a few Frenchmen, suspicious of their enemies, preferred to take their chances with the native Americans. Altogether, Ribault and about 350 of his officers and men lost their lives in the two massacres. The location of this event still carries today the name Matanzas, which is Spanish for "massacres." Menéndez had brilliantly but horrifically carried out his orders to wipe out the French incursion.
This act shocked Europeans even in that bloody age. In 1568, a French pirate, Dominique de Gourgues avenged Ribault in ghastly fashion. He attacked Spanish-held Fort Caroline, secured the garrison's surrender and then put all his prisoners to death.