He initiated a second attempt (the so-called Ivanovsky Canal between Yepifan and Ivan-Ozero) under the administration of Knyaz Matvey Gagarin. However it was too shallow, as it was on the upper Don and the upper Volga via the tributaries the Oka River, the Upa River, and the Shat River in the modern Tula Oblast. Between 1702 and 1707, twenty-four locks were constructed, and in 1707, about 300 ships passed through with difficulty. In 1709 due to financial difficulties caused by the Great Northern War, the project was halted. In 1711, under the terms of the Treaty of the Pruth, Russia left Azov and Peter the Great lost all interest in the canal, which was abandoned and fell into ruin. Over time, other projects for connecting the two rivers were proposed, but none were attempted. However, Dubovsko-Kachalinsky railway, which was horse-drawn railway and Volga–Don railway, which is now part of the South Eastern Railway were built in 1846 and 1852 respectively in order link the Volga and the Don at the shortest distance. They were 68 km and 73 km long respectively. The construction of today's Volga–Don Canal, designed by Sergey Zhuk's Hydroproject Institute, began prior to the Second World War, which interrupted the process. Construction works continued from 1948 to 1952 and the canal was opened on 1 June 1952. The canal and its facilities were built by about 900,000 workers including some 100,000 German POWs and 100,000 gulag prisoners. A day spent at the construction yard was counted as three days in prison, which spurred the prisoners to work. Several convicts were even awarded the Order of the Red Banner of Labour upon their release. Upon completion, the Volga–Don Canal became an important link in the Unified Deep Water Transportation System of the European part of the USSR. Operation The canal starts at the Sarepta backwater of the Volga, south of Volgograd where Lock No. 1 and the gateway arch are at . It ends in the Tsimlyansk Reservoir of the Don at the town of Kalach-na-Donu. The canal's highest elevation is the Varverovskoye (Barbarian) Reservoir between locks 9 and 10, above the Volga and above the Don rivers. It uses nine one-chamber canal locks on the Volga slope to raise/lower ships , and four canal locks of the same kind on the Don slope that raise/lower ships from river height. The overall dimensions of the locks are smaller