The Palazzo Altemps is located in the modern rione Ponte, part of the Campus Martius, a part of Ancient Rome that was developed beginning under the emperor Augustus. It is located directly north of the Piazza Navona. In the ancient period, this site was only 160 meters from the Ponte Elio, and was one of the two main marble ports on the Tiber River in Rome. The other was located in what is now Testaccio. In 1891, during the construction works to build the embankments that now hold back the Tiber River, the remains of this dock were uncovered. The marble was worked—into statuary, sculptural decoration, or architectural decoration—in shops, the ruins of which have been found in the zone between the church of Sant'Andrea della Valle, the Chiesa Nuova, and the Tiber River. A few of these ancient shops bear signs of hasty abandonment after the time of the emperor Trajan; tools and even unfinished statues were discovered in some cases.

There was also likely a temple to Apollo located in this area, over which has been built the church of Sant'Apollinare.In the Middle Ages and onwards, the Campus Martius was divided by the noble families of Rome. The east was controlled by the Ghibellines, led by the Colonna family, and the west by the Guelfs, led by the Orsini family. The division was mostly abandoned after the Great Schism in the 15th century, and the Campus Martius underwent a period of urbanization, leading to the Palazzo Altemps now visible.

Fonte: Wikipedia