During Spain's New World Empire, its mainland coastal possessions surrounding the Caribbean Sea and the Gulf of Mexico were referred to collectively as the Spanish Main. The southern portion of these coastal possessions were known as the Province of Tierra Firme (Spanish: Provincia de Tierra Firme), or the "Mainland Province" (as contrasted with Spain's nearby insular colonies). The Province of Tierra Firme, or simply Tierra Firme, was also called Costa Firme.