Ptahuacan was the capital city of the seven islands of Antillia, and the last surviving city of the Atlanteans by the time of the Hyborian Age. Ptahuacan was ruled by a caste of dark wizard-priests of the Hierarch of the Sacred Mysteries of Xotli. The priests ruled over the people through fear, and conducted dark rituals of mass sacrifice to their demon-god Xotli.
Ptahuacan was built on ascending levels, and the streets that ran along these levels were connected by sloping ramps and stairways. The city was a remarkable technical achievement, denoting a sophisticated culture with ancient traditions and well-developed artistic canons. The stonework was equal to that of the finest cities of the Hyborian kingdoms, and exceeded them in some measure through the massive proportions of the mighty temples and the meticulous precision of their masonry. The fantastic, temple-crowned ziggurat in the central square was as large as those found contemporaneously in Stygia, and reminiscent in style of the fanes of some of the sinister cults of Shem. They had been constructed over centuries of labour. Around the margins of the square ran a set of stone benches, rising tier upon tier until they could have held thousands of spectators facing the pyramid.
The myth of Antillia had spread to Hyboria, and according to Sigurd Redbeard, the Seven Cities of the Antilles were thought to have walls made of golden bricks, and streets paved with silver, and temple pyramids of orichalcum, although this did not prove to be the case when the crew of the Red Lion travelled there.