The Shrove Thursday celebration is closely related to the history of the Serenissima Republic of Venice, consequently to the victory over Ulrico, Patriarch of Aquileia.
Ulrico's troops had attacked Venice while the "Serenissima" was busy fighting another war against the Ducati of Padova and Ferrara. Italy was a lively place, at that time.
After the defeat, Ulrico had to pay the Venetian one bull and 12 pigs, as war reimbursement. So, from that moment on, the tradition was established of "executing" every year that same amount of animals in the San Marco square, and all the population participated to the feast, banquet, dances, acrobats.
Carnival was officially born.