West of the Provadia hills in Bulgaria is the valley of Shumen. The northern part of this valley belongs to the basin of the Provadia river, the southern to that of the river Kamtchia. The present railway line from Shumen to Kaspitchan serves as an ideal boundary between these two regions, but the two valleys are best known because of two historical sites, Preslav and Aboba (now Pliska).

The rivers of the Aboba plain have very little water during the summer season, but during winter and in time of heavy rains they overflow and cover great parts of the barren valley. The winter there is cold and severe, the surnmer dry and hot. In the plain, north of Kaspitchan railway station, are the ruins of Aboba. Eshberiich or Isperich (Asparuch), the younger son of Kurt (644–702), in his march southwards stopped there, and founded the first capital of the Bulgarian khans, later to become the magnificent Pliska.