Built in 25 BC, it is still in excellent condition and consists of two series of arches - one more central and two lateral minors - enclosing a parade ground. On both arcs the walkways of sentinels are visible. Central arch was intended for the passage of the carriages, while the two side to that of pedestrians. The three eastern gates were once closed by drawbridges gates. The two defensive towers with rectangular base have been rearranged in the course of time; the northern most noticeably, while the southern still preserves some Roman architectural features. In Middle Ages a chapel was built on the eastern central arch top, mentioned since the twelfth century, under which there was an oven for baking bread. Porta Pretoria consists of stone blocks set with shattered slate extracted from the bottom of Dora Baltea river.