The history of Uruguay comprises different periods: the pre-Columbian time or early history (up to the 16th century), the Colonial Period (1516–1811), the Period of Nation-Building (1811–1830), and the history of Uruguay as an independent country (1830). Native The earliest traces of human presence are about 10,000 years old and belong to the hunter-gatherer cultures of Catalanense and Cuareim cultures, which are extensions of cultures originating in Brazil. The earliest discovered bolas is about 7,000 years old. Examples of ancient rock art have been found at Chamangá. About 4,000 years ago, Charrúa and Guarani people arrived here. During precolonial times, Uruguayan territory was inhabited by small tribes of nomadic Charrúa, Chaná, Arachán, and Guarani peoples who survived by hunting and fishing and probably never reached more than 10,000 to 20,000 people. It is estimated that there were about 9,000 Charrúa and 6,000 Chaná and Guaraní at the time of first contact with Europeans in the 1500s. The native peoples had almost disappeared by the time of Uruguay's independence as a result of European diseases and constant warfare. European genocide culminated on 11 April 1831 with the Massacre of Salsipuedes, when most of the Charrúa men were killed by the Uruguayan army on the orders of President Fructuoso Rivera. The remaining 300 Charrúa women and children were divided as household slaves and servants among Europeans. Colonization During the colonial era, the present-day territory of Uruguay was known as Banda Oriental (east bank of River Uruguay) and was a buffer territory between the competing colonial pretensions of Portuguese Brazil and the Spanish Empire. The Portuguese first explored the region of present-day Uruguay in 1512–1513. The first European explorer to land there was Juan Díaz de Solís in 1516, but he was killed by natives. Ferdinand Magellan anchored at the future site of Montevideo in 1520. Sebastian Cabot in 1526 explored Río de la Plata, but no permanent settlements were established at that time. The absence of gold and silver limited the settlement of the region during the 16th and 17th centuries. In 1603, cattle and horses were introduced by the order of Hernando Arias de Saavedra, and, by the mid-17th century, their number had greatly multiplied. The first permanent settlement on the territory of present-day Uruguay was founded by Spanish Jesuits in 1624 at Villa Soriano on the Río Negro, where they tried to establish a Misiones Orientales system for the Charrúas.