The best-preserved and best-organized Jesuit mission in Brazil, São Miguel das Missões is an impressive, circa-1745 church built with reddish basalt slabs brought by the Guaranís from quarries miles away. The ruins are now a UNESCO World Heritage Site.
Jesuit missionaries moved into the upper Uruguay River basin around 1700. In the following decades the local Guaraní peoples were converted to Christianity, leading them to abandon their seminomadic lifestyle and congregate around the new missions—locally known as reduções (missionary communities). Seven of these existed in what is now Brazil, and several more were in Argentina and Paraguay—all linked by a closely knit trade and communication route. Historians have claimed that at the peak of their influence, the Jesuits actually created the first de facto country in the Americas, complete with a court system and elections. After the Treaty of Madrid granted rights over the lands and native peoples in the area to
the Portuguese crown, the Jesuits were under pressure to leave. Recurrent clashes with Portuguese militia precipitated the breakdown of the mission system, but the final blow came with the decree of expulsion of the Jesuit order from Portuguese territory. Most of the Guaranís dispersed back into unexplored country. This important historical period was depicted in the movie The Mission, starring Robert DeNiro, with several scenes shot at Iguaçu Falls.
A small museum on the grounds, designed by Lucío Costa (who was instrumental in the development of Brasília), holds religious statues carved by the Guaranís, as well as other pieces recovered from archaeological digs. Guided tours (in Portuguese) are given by appointment. Admission to the site includes a sound-and-light show that tells the mission's story, at 9 pm in summer and 7 pm in winter.
Other mission sites with ruins are São Lourenço and São Nicolau, about 70 km (43 miles) from São Miguel, but there's much less to be seen at these sites, which are not normally in tours. Across the border in Argentina, there's a larger and better preserved mission site, San Ignácio Mini.