trapdoors

The Prison was designed to have no doors, so the prisoners would be placed in the cells through movable stairs that descended from trapdoors in the chamber.

Years after the beginning of the construction of the Mariana City Council, the Ouro Preto City Hall was built with access doors to the Prison.

This probably influenced the alteration of the Mariana building, which turned the window of the middle cell into a door and created a corridor with an access door to each cell.