Thanks in part to Roland Joffe’s 1986 movie “The Mission,” there was a renewed surge of interest in the movement in the 1980s. Still, it was only in recent years that Paraguay, Argentina and Brazil began to restore and promote the missions — which, at their peak, had more than 100,000 residents and produced not just music and books, but also metal utensils and food for export — as tourist destinations.

Even now, the 30 existing missions are in widely varying states of repair, as I found during a weeklong journey through what was once known as the Jesuit Province of Paraquaria, and the infrastructure is hardly luxurious. I managed to visit more than half of the missions, also known in Spanish as “reducciones,” or “reductions,” on a roundabout tour that ended at Iguazú Falls, where Paraguay, Brazil and Argentina meet and the most dramatic scenes in “The Mission” were filmed.

QUITE quickly, I learned that all the missions — except the last to be built, in Santo Angelo in what is now Rio Grande do Sul, Brazil’s southernmost state — were laid out in identical fashion. A large church, classrooms and workshops dominated the southern side of a square, where community life was centered. The other three sides were occupied by family dwellings and by the cabildo, where the Guaraní town council, led by the chiefs, had its offices.

The point in visiting as many of the missions as possible was not just to be able to see the differences in style of the various Jesuit architects — some Spanish, others Italian or German — and the Guaraní artists and craftsmen they trained. Sadly, no single mission survived intact after the expulsion of the Jesuits, meaning that to obtain a complete picture of what a mission looked like then, it is necessary to visit several of them.

For instance, the mission at Jesús de Tavarangue, a few miles from my starting point in Trinidad, is the only one at which a bell tower, some 160 feet high, still stands. On a quiet Sunday morning, I climbed to the top and immediately understood that the commanding view of the rolling countryside it offered had both military and religious functions: not only to summon the faithful to Mass as often as three times a day, but also to warn residents when the bandeirantes, the dreaded slave traders from Brazil who raided the missions, were approaching.