The Orsini Palace in Monterotondo was built on the site of a previous, ancient fortress.
The Renaissance decorations were introduced in the 16th century, following the taste of the time.
It has been the headquarters for the municipality since 1890, restructured after crumbling in 1905 and damage from the Avezzano-Marsica earthquake in 1915.
The façade is in Romanic-Baroque style with a central bell tower at the last floor. There are two entrances; one for pedestrians on Via Giovagnoli, another for vehicles on Piazza Marconi. Both lead to an internal courtyard. This quadrangle is richly decorated in Baroque style, with columns and reliefs featuring crickets (grilli), the symbol of the Del Grillo family.
The Mayor's and his secretary's office holds frescoes and pannelled ceilings.
There is a second courtyard inside known as the well courtyard, because of a marble cistern made by a Roman workshop in the 16th century.