The Arx is one of the two small peaks that form the Capitoline Hill where some of the most important buildings of ancient Rome were erected. Here was the Auguraculum, the place where the Augurs, the soothsayers, observed the flights of birds and so interpreted the will of the gods. The Romans inherited these beliefs from the Etruscans.

The temple of Juno, which tradition records as dating back to the 4th century BC, was placed here where it could control the surrounding territory. For this reason, it was known as the temple of Juno Moneta. Although "moneta" in Latin means "warning", it came to mean "coin" because of the temple's proximity to the nearby mint. The word passed into the English lexicon as the word "money".