"Shadow", Chapter 3, Part 1

Speaking about the torturers' Matachin Tower, Severian says "the examination room was the propulsion chamber of the original structure". So their tower at least, and maybe all the structures in the Citadel, are converted spaceships. From other comments of Severian's, it's obvious that they were converted so long ago that no one knows why. Matachin is a Spanish word for a religious dancer. In Mexico, "The dancers are known for playing in rough-and-ready style a set drama based on the history of Montezuma. Even though the dances are based on this story, people who join the Matachines do it for a deeper religious purpose, since most of them join to venerate either Mother Mary (Our Lady of Guadalupe, Our Lady of Lourdes, Immaculate conception, etc.), a saint (the group usually chooses the saint that pertains to the church they belong to), or simply to worship Christ or God the Holy Trinity." So this is simultaneously a reference to a Catholic tradition and the Aztec culture. Were you aware that in Aztec religion existence is cyclical, with the sun dying at night to rise reborn in the morning? Or that the gods created four suns that were all destroyed, but an Aztec god sacrificed himself, and was reborn as the fifth sun so that humanity might live? Neither was I, but that last bit sounds vaguely familiar. Matachin also seems to mean a dance with swords and masks from Europe, probably Moorish in origin. Coincidentally enough, the torturers wear masks and use swords on ceremonial occasions.