The surviving ruins in the forum are probably not from the original building. Destroyed by earthquake, fire or the sacking of the city, the original "Regia" may have been rebuilt in a different location.
The rebuilt structure (which seems to have been transformed into a private residential building sometime during the seventh or eight centuries) had an irregularly formed enclosed courtyard that was paved in tuff with a wooden portico. The interior was divided into three rooms with entrance from the courtyard into the middle room.
The West Room was the shrine of Mars, sacrarium Martis, in which the ancilia (shields) of Mars were stored. Here, too, stood the lances that were consecrated to Mars, the hastae Martiae. According to legend if the lances in the Shrine of Mars start vibrating something terrible would happen. They are said to have vibrated on the night of 14 March 44 BC. Caesar, High Priest at the time, in spite of the vibrating lances left the Regia to attend at the meeting of the Senate where he was assassinated.
The East Room contained a sanctuary of Ops Consiva, so sacred that only the pontifex maximus and the Vestal Virgins were allowed to enter it.