in the region. The first permanent Spanish settlement was founded in 1624 at Soriano on the Río Negro. In 1669–71, the Portuguese built a fort at Colonia del Sacramento (Colônia do Sacramento). Montevideo was founded by the Spanish in the early 18th century as a military stronghold in the country. Its natural harbor soon developed into a commercial area competing with Río de la Plata's capital, Buenos Aires. Uruguay's early 19th-century history was shaped by ongoing fights for dominance in the Platine region, between British, Spanish, Portuguese and other colonial forces. In 1806 and 1807, the British army attempted to seize Buenos Aires and Montevideo as part of the Napoleonic Wars. Montevideo was occupied by a British force from February to September 1807. Independence struggle In 1811, José Gervasio Artigas, who became Uruguay's national hero, launched a successful revolt against the Spanish authorities, defeating them on 18 May at the Battle of Las Piedras. In 1813, the new government in Buenos Aires convened a constituent assembly where Artigas emerged as a champion of federalism, demanding political and economic autonomy for each area, and for the Banda Oriental in particular. The assembly refused to seat the delegates from the Banda Oriental, however, and Buenos Aires pursued a system based on unitary centralism. As a result, Artigas broke with Buenos Aires and besieged Montevideo, taking the city in early 1815. Once the troops from Buenos Aires had withdrawn, the Banda Oriental appointed its first autonomous government. Artigas organized the Federal League under his protection, consisting of six provinces, four of which later became part of Argentina. In 1816, a force of 10,000 Portuguese troops invaded the Banda Oriental from Brazil; they took Montevideo in January 1817. After nearly four more years of struggle, the Portuguese Kingdom of Brazil annexed the Banda Oriental as a province under the name of "Cisplatina". The Brazilian Empire became independent of Portugal in 1822. In response to the annexation, the Thirty-Three Orientals, led by Juan Antonio Lavalleja, declared independence on 25 August 1825 supported by the United Provinces of the Río de la Plata (present-day Argentina). This led to the 500-day-long Cisplatine War. Neither side gained the upper hand and in 1828 the Treaty of Montevideo, fostered by the United Kingdom through the diplomatic efforts of Viscount John Ponsonby, gave birth to Uruguay as an independent state. 25 August is celebrated as Independence Day, a national holiday.