Porta Gemina, Roman city gate in Ascoli Piceno, Italy.

Porta Gemina is a first-century BC Roman gate built of squared travertine blocks without mortar. It has two arches on three square piers 1.80 m wide, with a total height of 6.75 m and width of 9.47 m; each arch is 5.70 m high and 2.95 m wide. A cornice links the arches and continues onto the side piers, and the grooves that held the portcullis are still visible inside the arches.

Built in the first century BC, the gate served as an entrance checkpoint for the Via Salaria, a major trade route connecting Rome to the Adriatic coast. It formed part of the city's defensive system and retained importance through several historical periods.

The gate displays Roman construction methods visible in its solid stone structure and two matching arches. Visitors notice the craftsmanship when passing beneath the passages, which still serve as the eastern entrance to the old town.

The gate stands at the end of Via Porta Romana, near the Tronto river and the slope of the Annunziata hill. The two arches are open and can be walked through; the 13th-century circular tower with battlements rises alongside. The site is outdoors and can be visited at any time.

The gate displays precise mathematical proportions in its two arches, demonstrating the advanced knowledge of Roman builders. This careful design allowed the structure to remain stable for more than 2000 years.