The Rathma Square is a dungeon uberquest accessible by reaching the Bastion of the Triune via the southwestern stairs in the Profane Cells in Caldeum, then taking the stairs immediately next to the entrance. It is home to the immortal Gore Crawlers, which cannot be killed permanently, as well as the boss Lord Primus.
Back in the days when Kurast was the centre of civilisation and black magic was not yet frowned upon, this was where the priests of Rathma - the necromancers - practiced their art. The place was abandoned when the religion of Zakarum took over the city and banned pagan magic, making it the perfect hiding place for an ancient evil bent on taking out the Church from within. Primus, son of Mephisto, was the leader of the Cult of the Triune in ages past before its destruction. His efforts to rebuild the Triune were shut down by the crusaders of Zakarum, but he remains a formidable foe, doubly so in the home city of the Zakarum.