Isthmus of Perekop
A large portion of the line ran along the Dnieper River, from just west of Smolensk to the Black Sea. The line left the banks of the Dnieper only where another major tributary offered similar defensive capabilities. In the south, where the Dnieper curved (western Dnipropetrovsk Oblast) to the west, it was decided to construct the line east of the Dnieper in order to avoid the evacuation or isolation of the Crimea. The Dniper line offered no protection to the Crimea's Isthmus of Perekop link with the mainland. In the north, the line was to have been constructed roughly from Vitebsk to Pskov, where it then followed the west bank of Lake Peipus, and its river delta to the Baltic Sea at Narva.