The Arengo was the name of the assembly that ruled San Marino from the fifth century A.D. to 1243, and of the popular councils which regulated the political life in Northern Italy free comuni in the Middle Ages as well.
It was made up of the heads of San Marino's Great families and had no leader or fixed meeting place.
By the early 13th century the Arengo had become so dysfunctional that the citizens of San Marino decided to elect their own assembly, which they called the Grand and General Council.
After the death of the founders, the community was governed by a small leaderless collection of monks based around the church of St. Agatha on the top of Monte Titano.
With such a large expansion of population it became clear that San Marino could not remain without a central structure so the Arengo was formed; based on the original Roman Senate, it was made of the head of each of the Great Families.