The Ries is in fact a crater caused by a meteorite 14.8 million years ago. The depression has a circular shape and is 25 km in diameter. The bottom of the crater is about 100-150 m below the brink. The city of Nördlingen is located in the middle of the crater.
The word "Ries" is not a German word; it is believed that the term is derived from Raetia, since the tribe of Raetians lived in the area in pre-Roman times. The addition "Nördlinger" is actually redundant, as there is no other place called Ries.
In 1960 two American scientists, Eugene Shoemaker and Edward Chao, proved that the depression was caused by a meteorite. Until then it was assumed, that the Ries was of volcanic origin.
For human settlement within the Ries region, see Donau-Ries.