The term CITY ON THE OKA RIVER can be solved by the four-letter word OREL. Orel is a city in Russia located on the Oka River, a tributary of the Volga River. It is the administrative center of Oryol Oblast and is one of the oldest cities in the region. Orel was founded in 1566 and has a population of about 315, 000 people. It is an important industrial and cultural center in the region and is home to several universities and museums.