The about 74 kilometres long Erma River (in Serbia known as Jerma River) is a tributary of the Nišava River and originates near the Vlasinsko lake in southeastern Serbia. The river flows along the eastern slopes of Gramada and Ruy mountain towards Tran (Bulgaria).
In a distance of about 3 km in the north of Tran the river created the Erma Gorge (Transko zhdrelo). The gorge is about 100 meters long and about 5 meters wide at its narrowest part. The Erma Gorge was declared a natural landmark on 26th July 1961 in order to preserve the unique rock formations.
After 26 kilometres in western Bulgaria the river re-enters Serbia again and has created an about 15 km long canyon between the Vlaska Planina (1'442 m) and Greben Peak (1'337 m).
Bulgaria 1968, Erma Gorge in Bulgaria.
The stamp was issued in the series "Landscapes".
Serbia 2001, Jerma Canyon in Serbia.
The stamp was issued in the series "Cept".