While sugar cane dramatically increased Spain's earnings on the island, large numbers of the newly imported slaves fled into the nearly impassable mountain ranges in the island's interior, joining the growing communities of "cimarrónes"—literally, 'wild animals'. By the 1530s, "cimarrón" bands had become so numerous that in rural areas the Spaniards could only safely travel outside their plantations in large armed groups. Beginning in the 1520s, the Caribbean Sea was raided by increasingly numerous French pirates. In 1541 Spain authorized the construction of Santo Domingo's fortified wall, and in 1560 decided to restrict sea travel to enormous, well-armed convoys. In another move, which would destroy Hispaniola's sugar industry, in 1561 Havana, more strategically located in relation to the Gulf Stream, was selected as the designated stopping point for the merchant "flotas," which had a royal monopoly on commerce with the Americas. In 1564, the island's main inland cities Santiago de los Caballeros and Concepción de la Vega were destroyed by an earthquake. In the 1560s English buccaneers joined the French in regularly raiding Spanish shipping in the Americas.