Development of the Sula river frontier of the Pereyaslavl land

An extended log fortification structure and a chain of open settlements fromwhere lookouts could spot the enemy and send information on incursions to the metropolis were built on the steppe bank of the Lower Sula at the end of the 10th century. In thefirst half of the 11th century the wall fell into disrepair, but because of continuous Polovetsraids in the second half of the century a defensive line consisting of eight fortresses wasbuilt. A burst of defensive structure construction at the end of the 11th - early 12th centuries completed the Lower Sula section. Because of the river forests the protection of themiddle reaches of the Sula required fewer efforts, while revamping of the land ownershipupstream that lasted for half a century put an end to the construction of the defensive linein Pereyaslavl. By 1125 65 % of the known fortifications had already been built on theSula. The former line turned into an echelon border. The Pereyaslavl Torks with their lighthorse cavalry units settled down along the border in substantial numbers as well. Theirtactics and weapons were comparable to those of the Polovets. Thanks to Vladimir Mono-makh, round fortresses that reinforced the priority of artificial obstacles, which were notassociated with surface features, were built as well, giving an opportunity to protect theplains. In terms of their size, fortresses form compact groups. It reflects standardization ofconstruction in accordance with a preset plan based on defensive and social requirements.