We do not know exactly where this piazza gets its name from, but being the point where roads from the Quirinal Hill converge, it certainly offers a visual synthesis of the millenary history of Rome. Let's take it in chronological order.
In the central garden, you can see some blocks of tufa. Indicating part of the boundary of pre-republican Rome, these blocks are the remains of the 4th century Servian walls.
The great hall of Trajan's Market also dates back to ancient Rome, but only to imperial times. Although today this space is used for exhibitions, it used to be a place for the Empire's business deals and commodity trading.
The Torre delle Milizie was annexed to Trajan's Market in 1927. This tower was erected by the Conti family at the beginning of the 13th century, only to be acquired by Pope Boniface VIII a few decades later. He fortified it as a means of countering the power of his most bitter enemies, the Colonna family. During the earthquake of 1348, part of the tower fell down and it took on the lean it has today.
On the same side of the street there is the façade of the church of Santa Caterina, built in the first decades of the 17th century.
is closed by the perimeter wall of Villa Aldobrandini, one of the princely villas on the Quirinal Hill whose gardens were destroyed by the construction of Via Nazionale.