“Rocca Traversa” or simply “Traversa”, as documented in the Middle Ages, was built after 1153 by the will of Pope Eugene III. Two epigraphs still in situ inform with an identical text on its construction, aimed at using a triangular bastion of the late ancient walls of Terracina (5th-6th century). However, the epigraphic text hides the recipients of the operation: the Frangipane. In fact, the relationship between the Frangipane and the “Traversa” crosses the second half of the 12th century and the tower progressively rises as a symbol of their dominion over Terracina, so much so that it was destroyed in 1202 before returning under papal control in 1207. At the same time, the monument shows also a functional transformation from tower into urban garrison. The authors of the contribution focused on the origins of the “Traversa”, both from a historical point of view (through the textual analysis of the two epigraphs), as well as an archaeological and urbanistic point of view, in order to give an exhaustive picture of the oldest baronial settlement wich survived in Southern Lazio.