The Devil's Dykes (Hungarian: Ördögárok) , also known as the Csörsz árka ("Csörsz Ditch") or the Limes Sarmatiae (Latin for "Sarmatian border"), are several lines of Roman fortifications built mostly during the reign of Constantine I (312-337), stretching between today's Hungary, Romania and Serbia.

The fortifications consisted of a series of defensive earthen ramparts-and-ditches surrounding the plain of the Tisia (Tisza) river. They stretched from Aquincum (within modern Budapest) eastwards along the line of the northern Carpathian mountains to the vicinity of Debrecen, and then southwards to Viminacium (near modern Stari Kostolac).

They were probably designed to protect the Iazyges, a Sarmatian tribe that inhabited the Tisza plain and had been reduced to tributary status by Constantine, from incursions by the surrounding Goths and Gepids.

Some elements of the fortifications, however, date from the 2nd century AD, and probably constituted an earlier defensive line constructed under emperor Marcus Aurelius (ruled 161-80) at the time of the Marcomannic Wars, the previous occasion that the Tisza plain was occupied by the Romans.