Pyramids of Mars

The Pyramids of Mars, the main pyramid being called the Pyramid of Horus, (PROSE: Doctor Who and the Pyramids of Mars) or the singular Pyramid of Mars, were several pyramids established on Mars by the Osirans to house the Eye of Horus and keep Sutekh trapped on Earth. Possessing Marcus Scarman and the Fourth Doctor, Sutekh orchestrated the Eye's destruction, temporarily freeing him before the Doctor trapped him in a time tunnel via an Osiran lodestone. (TV: Pyramids of Mars)

The Horus ruins were later discovered a few years prior to 3984. (PROSE: Legacy) Bernice Summerfield visited the Pyramid of Horus and tried assisting the Seventh Doctor when Sutekh gained his freedom again. (AUDIO: The Pyramid of Sutekh)

A Martian ambassador was dispatched to Earth from Mars after the disappearance of all but one of Mars's pyramids. (PROSE: The Book of the Enemy)

The Tremas Master made reference to the Martian Pyramids. (AUDIO: The Auton Infinity)

Behind the Scenes
Despite the title Pyramids of Mars being plural, the serial's dialogue only ever refers to the "Pyramid of Mars" although Sutekh also cites an antechamber being under the "main" pyramid. The novelisation however refers to the titular location in plural.