Evidence of the Roman heritage of Reims greets anyone arriving by train as, just across the street is the Porte de Mars, one of four original gates to the city walls. This one is pretty impressive: over a hundred feet long and over 40 feet high, with three triumphal archways. It likely dates from the 3rd or 4th Century.
There is also a cryptoporticus, or underground gallery, probably also from the 3rd Century, further into the center of town. At times it is open to the public but not when we were there, but we could see the outer walls below street level. It appears to be pretty well preserved and was likely the foundational support for the forum which would have stood here in those days
Named after a nearby non-extant Temple of Mars, this Roman-period structure was a triumphal arch built in the 3rd century AD. It once led into the cardo maximus, the road which cut through the city of Durocortorum, i.e. Roman Reims, from the north into the Forum. In Mediaeval times, the arch was incorporated into the construction of fortified ramparts and was turned into the northern city gate, but it managed to retain the reference to Mars in its name. Although partially restored, Porte Mars is fairly well preserved, with many of the pagan decorations and sculptures clearly discernible, particularly on the northwestern side, as shown in the attached photographs. However, in its original design, the gate is thought to have had a second level topped by large bronze sculpture of horses (see next tip). The gate was saved from destruction during 19th century urban planning, when the ramparts were removed to create the surrounding park and boulevards.