Syrmia is a region of the southern Pannonian Plain, which lies between the Danube and Sava rivers. It is divided between Serbia and Croatia. Most of the region is flat, with the exception of the low Fruška gora mountain stretching along the Danube in its northern part.

The Pannonian Basin, or Carpathian Basin, is a large sedimentary basin situated in southeast Central Europe. After the WW1 and Treaty of Trianon, the geomorphological term Pannonian Plain became more widely used for roughly the same region though with a somewhat different sense, with only the lowlands, the plain that remained when the Pliocene Epoch Pannonian Sea dried out.