Fortified lines played a major role in Muscovy's southern frontier defense strategy. The great scale of these fortifications projects testified to the Muscovite state's considerable powers of resource mobilization.
The defense of Muscovy's southern frontier relied heavily upon long fortified lines linking garrison towns and serving as stations for the corps of the southern frontier field army. These lines were never intended to be impermeable walls keeping out the Tatars, but rather a supporting infrastructure for reconnaissance patrols, signaling, and corps movements beyond or behind the defense line. The gradual extension of these defense lines deeper into the steppe over the course of the late sixteenth and seventeenth centuries reflected the Muscovite state's successes in the military colonization of its southern frontier and in its command and control of much larger field armies.
To stop the Crimean Tatars from invading central Muscovy, it had become necessary by 1512 to station several thousand troops along the Bank Line (Bereg), an especially vulnerable 250-kilometer(155.3-mile) stretch of the Oka between Kolomna and Kaluga, every spring and summer. By century's end the Abatis Line (Zasechnaya cherta), an additional network of forest abatis and fortifications almost 1,000 kilometers (620 miles) in span, had arisen another 100 kilometers (62 miles) farther south; the field army was restationed along it, providing central Muscovy with greater defense in depth and also encouraging military colonization of the forest-steppe zone. From 1637 to 1658 a new Belgorod Line was built along most of the southern edge of the forest-steppe, from Akhtyrka in northeastern Ukraine to Chelnavsk; it consisted of earthen fortifications built in the new Dutch manner, as well as abatis, and linked twenty-five garrison towns. From 1646 it became the new line of deployment for the corps of the southern field army as well as a place d'armes for aggressive operations down the Don (against the Crimean Khanate and the Ottoman fortress of Azov) and in Ukraine (against the Commonwealth during the Thirteen Years War). In 1679–1680 most of the steppe along the Northern Donets and Oskol rivers was enclosed behind yet another new line, the Izyuma Line, another 160 kilometers (99.42 miles) southeast of the Belgorod Line.
See also: crimean tatars; military, imperial era; muscovy; thirteen years' war