structural:expansion, quality:correction
Crimean raids

In the later years of Ivan's reign, the southern borders of Muscovy were disturbed by Crimean Tatars, mainly to capture slaves. (See also Slavery in the Ottoman Empire.) Khan Devlet I Giray of Crimea repeatedly raided the Moscow region. In 1571, the 40,000-strong Crimean and Turkish army launched a large-scale raid. The ongoing Livonian War made Moscow's garrison to number only 6,000 and could not even delay the Tatar approach. Unresisted, Devlet devastated unprotected towns and villages around Moscow and caused the Fire of Moscow (1571). Historians have estimated the number of casualties of the fire to be 10,000 to 80,000.

To buy peace from Devlet Giray, Ivan was forced to relinquish his claims on Astrakhan for the Crimean Khanate, but the proposed transfer was only a diplomatic maneuver and was never actually completed. The defeat angered Ivan. Between 1571 and 1572, preparations were made upon his orders. In addition to Zasechnaya cherta, innovative fortifications were set beyond the Oka River, which defined the border.

The following year, Devlet launched another raid on Moscow, now with a numerous horde, reinforced by Turkish janissaries equipped with firearms and cannons. The Russian army, led by Prince Mikhail Vorotynsky, was half the size but was experienced and supported by streltsy, equipped with modern firearms and gulyay-gorods. In addition, it was no longer artificially divided into two parts (the "oprichnina" and "zemsky"), unlike during the 1571 defeat. On 27 July, the horde broke through the defensive line along the Oka River and moved towards Moscow. The Russian troops did not have time to intercept it, but the regiment of Prince Khvorostinin vigorously attacked the Tatars from the rear. The Khan stopped only 30 km from Moscow and brought down his entire army back on the Russians, who managed to take up defense near the village of Molodi. After several days of heavy fighting, Mikhail Vorotynsky with the main part of the army flanked the Tatars and dealt a sudden blow on 2 August, and Khvorostinin made a sortie from the fortifications. The Tatars were completely defeated and fled. The next year, Ivan, who had sat out in distant Novgorod during the battle, killed Mikhail Vorotynsky.