The Gulf of Mexico is the eleventh largest body of water in the world. Considered a smaller part of the Atlantic Ocean, it is an ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. The shape of its basin is roughly oval and approximately 810 nautical miles wide and filled with sedimentary rocks and debris. It is part of the Atlantic Ocean through the Florida Straits between the U.S. and Cuba, and with the Caribbean Sea (with which it forms the American Mediterranean Sea) via the Yucatan Channel between Mexico and Cuba. Tidal ranges are extremely small due to the narrow connection with the ocean. The gulf basin is approximately 615,000 mi² . Almost half of the basin is shallow intertidal waters. At its deepest it is 14,383 ft at the Sigsbee Deep, an irregular trough more than 300 nautical miles. It was probably formed approximately 300 million years ago as a result of the seafloor sinking.
Although Christopher Columbus was credited with the discovery of the Americas by Europeans, the ships in his four voyages never reached the Gulf of Mexico. Instead, Columbus sailed into the Caribbean around Cuba and Hispaniola.
The first European exploration of the Gulf of Mexico was Amerigo Vespucci in 1497. He followed the coastal land mass of central America before returning to the Atlantic Ocean via the Straits of Florida between Florida and Cuba. In his letters, Vespucci described this trip, and once Juan de la Cosa returned to Spain, a famous world map, depicting Cuba as an island, was produced.
In 1506, Hernán Cortés took part in the conquest of Hispaniola and Cuba, receiving a large estate of land and Indian slaves for his effort. In 1510, he accompanied Diego Velázquez de Cuéllar, an aide of the governor of Hispaniola, in his expedition to conquer Cuba. In 1518 Velázquez put him in command of an expedition to explore and secure the interior of Mexico for colonization.
In 1517, Francisco Hernández de Córdoba discovered the Yucatán Peninsula. This was the first European encounter with an advanced civilization in the Americas, with solidly-built buildings and a complex social organization which they recognized as being comparable to those of the Old World; they also had reason to expect that this new land would have gold. All of this encouraged two further expeditions, the first in 1518 under the command of Juan de Grijalva, and the second in 1519 under the command of Hernán Cortés, which led to the Spanish exploration, military invasion, and ultimately settlement and colonization known as the Conquest of Mexico. Hernández did not live to see the continuation of his work: he died in 1517, the year of his expedition, as the result of the injuries and the extreme thirst suffered during the voyage, and disappointed in the knowledge that Diego Velázquez had given precedence to Grijalva as the captain of the next expedition to Yucatán.
In 1523, Ángel de Villafañe sailed toward Mexico City, but was shipwrecked en route along the coast of Padre Island, Texas in 1554. When word of the disaster reached Mexico City, the viceroy requested a rescue fleet and immediately sent Villafañe marching overland to find the treasure-laden vessels. Villafañe traveled to Pánuco and hired a ship to transport him to the site, which had already been visited from that community. He arrived in time to greet García de Escalante Alvarado (a nephew of Pedro de Alvarado), commander of the salvage operation, when Alvarado arrived by sea on July 22, 1554. The team labored until September 12 to salvage the Padre Island treasure. This loss, in combination with other ship disasters around the Gulf of Mexico, gave rise to a plan for establishing a settlement on the northern Gulf Coast to protect shipping and more quickly rescue castaways. As a result, the expedition of Tristán de Luna y Arellano was sent and landed at Pensacola Bay on August 15, 1559.
On December 11, 1526, Charles V granted Pánfilo de Narváez a license to claim what is now the Gulf Coast of the United States, known as the Narváez expedition. The contract gave him one year to gather an army, leave Spain, be large enough to found at least two towns of 100 people each, and garrison two more fortresses anywhere along the coast. On April 7, 1528, they spotted land north of what is now Tampa Bay. They turned south and traveled for two days looking for a great harbor the master pilot Miruelo knew of. Sometime during these two days, one of the five remaining ships was lost on the rugged coast, but nothing else is known of it.
In 1697, Pierre Le Moyne d'Iberville sailed for France and was chosen by the Minister of Marine to lead an expedition to rediscover the mouth of the Mississippi River and to colonize Louisiana which the English coveted. Iberville's fleet sailed from Brest on 24 October 1698. On January 25, 1699, Iberville reached Santa Rosa Island in front of Pensacola founded by the Spanish; he sailed from there to Mobile Bay and explored Massacre Island, later renamed Dauphin Island. He cast anchor between Cat Island and Ship Island; and on February 13, 1699, he went to the mainland, Biloxi, with his brother Jean-Baptiste Le Moyne de Bienville. On May 1, 1699, he completed a fort on the north-east side of the Bay of Biloxi, a little to the rear of what is now Ocean Springs, Mississippi. This fort was known as Fort Maurepas or Old Biloxi. A few days later, on May 4, Pierre Le Moyne sailed for France leaving his teenage brother, Jean-Baptiste Le Moyne, as second in command to the French commandant.