The Capitoline Triad oversaw the affairs of Rome and her people. Jupiter Optimus Maximus (Brightest and Best) protected the state. In addition, Juno Regina was the guardian of Rome. Together, They guided the affairs of the Roman people. Meanwhile, Minerva was the Patron of Doctors and the Arts.
After the wars with the Sabines, King Tarquin Priscus asked the Deities of a shrine on Capitoline Hill to move so that he could build a temple to Jupiter Optimus Maximus. In exchange for their leaving, he promised Them a new temple elsewhere (exauguration). (Note 1) All the Gods did except for Terminus, the God of Boundaries. The Romans regarded this as a good omen. The new temple was dedicated to Jupiter, Juno Regina, and Minerva (the Capitoline Triad). (However, a part of it remained a shrine to Terminus.) On the Ides of September, the praetor maximus (head magistrate) would drive a nail into the wall of the temple (cella Iovis). This was to ward off the plague for another year.
The main temple for the Capitoline Triad had three rooms with each God having their own space. Jupiter Optimus Maximus occupied the center cella (room), with Juno Regina on the left and Minerva on the right. Although the temple was built during the time of Roman Kings, it was dedicated by the first Consul of the Roman Republic.
Note 1. Exauguratio (exauguration) is to change the purpose of a sacred site. It usually involves asking the God who resides there to move elsewhere.
Read also from 2016: Gods and Politics: Civics from the Roman Triads