The Lupercal's Court was a large strategium room located on the starship Vengeful Spirit.
This chamber was created in the waning years of the Great Crusade and during the early start of the Horus Heresy. It was made under the explicit orders of Warmaster Horus who required a large room through which his war council was capable of assembling in. Horus himself sat in a central throne which seemed too small to contain his large frame. Numerous commanders were present with the former members of the Mournival typically standing by the side of the Warmaster.
When the Imperial Expedition of Horus began to secretly prepare for their Heresy against the Emperor, the Remembrancer Order had their movements through the ships restrained with any requests being sent to the Office of the Lupercal's Court. This allowed Horus to keep the civilian population of the fleet contained and trapped so that he was capable of eliminating them when he openly declared his war against his father.
During the assault on the rebels in the Isstvan system, Death Guard Primarch Mortarion, World Eaters Primarch Angron and Emperor's Children Lord Commander Eidolon assembled in Lupercal's Court in order to gain instructions on how to take the system. 1