According to tradition, it has built with Roman people's money.Hence the name of the place. In fact the square is the result of a long process of stratification of successive constructions the present layout dates from the beginning og the I9th century, and it was designed by the architect Giuseppe Valadier It is composed of two hemicycles where two exedras are adomed with sphinxed, allegorical figures of the season, and fountains with sculptures.The opening onto the sqare better known as Trident, where the Via del Babuino, Via del Corso and Via dl Ripetta begin, goes hack to the i6th century in spite of the rationality of its layout, several capital executions took place in it.