Jupiter Optimus Maximus was the king of the gods and the god of the sky and thunder and the divine witness of oaths, the sacred trust to which justice and government depended on. Jupiter was the chief god of the Roman state throughout the Republican and Imperial eras. He was the husband of Juno Moneta and the father of Mars Ultor.
The Greeks envisioned Zeus as a powerful and proud being, while the Romans envisioned Jupiter as a more formal and responsible.
Jupiter is the supreme god of the Roman pantheon, called dies pater, which means "shining father." He is a god of light and sky, and protector of the state and its laws. The Romans worshiped him especially as Jupiter Optimus Maximus (the best and the greatest). This name refers not only to his rule over the Universe, but also to his function as the god of the state who distributes laws, controls the realm, and makes his will known through various Oracles.
He had a temple on the capitol, along with Juno and Minerva, but he was the most prominent of this Capitoline triad. His temple was not only the most important sanctuary in Rome; it was also the center of Roman political life. Here official offerings were made, treaties were signed and wars were declared, and the triumphant generals of the Roman army came here to give their thanks.
Faced by a period of bad weather endangering the harvest during one early spring, King Numa resorted to the scheme of asking the advice of the god by evoking his presence. He succeeded through the help of Picus and Faunus, whom he had imprisoned by making them drunk.
After Numa skilfully avoided the requests of the god for human sacrifices, Jupiter agreed to his request to know how lightning bolts are averted, asking only for the substitutions Numa had mentioned: an onion bulb, hairs and a fish.
Jupiter promised that at the sunrise of the following day he would give to Numa and the Roman people pawns of the imperium. The following day, after throwing three lightning bolts across a clear sky, Jupiter sent down from heaven a shield.
Since this shield had no angles, Numa named it ancile; because in it resided the fate of the imperium, he had many copies made of it to disguise the real one. He asked the smith Mamurius Veturius to make the copies, and gave them to the Salii. As his only reward, Mamurius expressed the wish that his name be sung in the last of their carmina.