In the Roman calendar, March was sacred to Mars. The “jumping priests,” or Salii began the Festival of the Salii on March 21 with a purification of the sacred trumpets that the Romans carried off to war. That date was originally the Roman New Year’s Day because it was the start of the growing and campaign season.
On March 21, the Salii marched to the Regia taking the bronze Ancilia, the sacred shield that had fallen down from heaven, and its 11 copies. They danced through the streets carrying poles with the shields mounted on them in their left hands. With their other hand, they banged the shields with a drumstick. Even in the time of Cicero, the Carmen Saliare they sang was so ancient that he could not understand it.
At the end of each night, they would stop at a place to be feasted before starting up again the next day. This festival would end on March 24 when they would return to the Regia and return the shields.
Found at Wikipedia