According to Livy, the temple was vowed to the god Mars in the aftermath of the Roman defeat at the Battle of the Allia in 390 BCE by the Senones.
This stone was used as part of a ceremony of Etruscan origin called the aquaelicium which sought to produce rain in times of drought.
The stone was removed from the temple by the pontifices, and taken by procession to the Capitoline Hill, and a sacrifice was made to the god Jupiter, petitioning him to send rain.
It was in this area around the temple that the soldiers of the Republic would assemble before heading off to fight their wars, and it was here that they would return to lay down their arms prior to re-entering the city.
[4] It was also the spot where, on 15 July, the Transvectio equitum procession would commence, to commemorate the victory at the Battle of Lake Regillus.