Local patriots under José Gervasio Artigas issued the Proclamation of 26 February 1811 which called for a war against the Spanish rule. With the help from Buenos Aires, Artigas defeated Spaniards on May 18, 1811 at the Battle of Las Piedras and began Siege of Montevideo. At this point Spanish viceroy invited Portuguese from Brazil to launch a military invasion of Banda Oriental. Afraid to lose this province to the Portuguese, Buenos Aires made peace with the Spanish viceroy. British pressure persuaded the Portuguese to withdraw in late 1811, leaving the royalists in control of Montevideo. Angered by this betrayal by Buenos Aires, Artigas with some 4000 supporters retreated to Entre Ríos Province. During the Second Banda Oriental campaign in 1813, Artigas joined José Rondeau's army from Buenos Aires and started the second siege of Montevideo, resulting in its surrender to Río de la Plata.