If you saw the film "The Mission" (http://en.wikipedia.org/wiki/The_Mission_%28film%29) with Robert De Nio, you can have an idea of this place. It´s a sad aprt of our History.
"In 1570, treaty of Madrid ruled the reductions localized in the brazilian territory become property of the Portugal Kingdon. Natives didn´t accept and began the war called Guaranitical (from the word Guarani, native) Wars. Native resistence was coordinated by the native 'Sepe Tiaraju' and his historical slogan: "This land has an owner!". Although navites was victorious in the early begining the war against luso and hispanic troops due to knowledge of the terrain, more entusiasm and tactical mobility, the troops of the kingdon prevail due to technological superiorty and fire power."
see more in the sites: http://rodrigomochileiro.blogspot.com/2006_06_01_archive.html and
http://en.wikipedia.org/wiki/S%C3%A3o_Miguel_das_Miss%C3%B5es