An agger is an ancient Roman embankment or rampart, or any artificial elevation. It is a Latin word.[1]
It is especially used for the raised and cambered embankment carrying a Roman road. The agger was constructed by excavating the line of the road, building a firm foundation, refilling and compressing the soil, adding more soil from digging drainage ditches or fosses on one or both sides of the road, then surfacing with graded layers of stone and cobbles. The course of a Roman road can often be traced today by the distinctive line of the agger across the landscape.
A well-known example is the Agger Servianus, a part of the Servian walls of Rome, which protected the city on its most vulnerable side, the Campus Esquilinus. It consisted of a double rampart bearing formidable fortifications.