In late May news of the pending invasion reached Moscow. Nesin (2015) says it was the largest Tatar army in the fifteenth century. One faction wanted to flee north, but was overruled. In June Ivan sent troops south to the Oka: to
Serpukhov under his son
Ivan the Young, to
Tarusa under his brother Andrey the Less, and under Ivan himself to
Kolomna. Tatar scouting parties soon appeared south of the Oka. Russian outposts reported that Akhmed was tending northwest so Russian troops were moved west toward
Kaluga. Forces from Tver moved toward the Ugra. Around 30 September Ivan returned to Moscow to meet with his bishops and
boyars and major decisions were made. The quarrel with his brothers was settled and their troops began moving toward the Oka. The state treasury and royal family were moved north to
Beloozero, and some cities were evacuated. Vasily Nozdrovaty and the exiled Crimean khan
Nur Devlet were sent east down the Oka and Volga to attack Akhmed in the rear. Meanwhile, Akhmed had moved northward between the upper Don and Oka and at an uncertain date made camp at
Vorotynsk just south of the Ugra-Oka junction on the west bank of the Oka. Here he waited for Casimir, who never came. Casimir was tied down fighting the Crimeans in Podolia, but he may have had other reasons for not coming. On 3 October Ivan moved to Kremenets (now in modern
Medynsky District) to watch the front. Nesin (2015) gives the Russian front as 60 versts (kilometers), but does not specify its start and end points. On 6–8 October Akhmed moved his troops up to the Ugra. Fighting began at one o'clock on the eighth and continued for almost four days. Attempts to cross the river failed, largely because of Russian missiles, and because the river was wide enough to make Tatar arrows ineffective. The battlefield extended five kilometers along the Ugra from its mouth westward. Akhmed withdrew two versts (kilometers) south to a place called Luza. He then tried to secretly move his troops to a place called 'Opakhov', but his movement was detected and the crossing blocked. Ivan began negotiations with Akhmed, which led nowhere, but gave Ivan time to bring up more troops. Both sides spent the next month watching each other across the river. It was getting late in the season and both sides knew that once the river froze solid it would no longer be a barrier. Akhmed could concentrate his forces and break the thin Russian line at any point. Ivan's best plan was to pull back and concentrate his force. On 26 October Ivan began moving troops from the Ugra northeast to Kremenets and then east to
Borovsk. Here he had a good defensive position to protect Moscow and could strike in any direction if Akhmed chose to advance. Akhmed expected
Casimir IV Jagiellon to join him with Lithuanian reinforcements, but Casimir faced a revolt at home and never came. Instead of advancing, on 8 November Akhmed began to withdraw. News of the retreat reached Ivan on 11 November. In his retreat, Akhmed raided twelve Lithuanian towns, including
Mtsensk. His son Murtaza raided some villages south of the Oka until the Russians drove him off. On 28 November Ivan returned to Moscow. In January 1481 Akhmed was killed by
Ibak Khan. ==Reasons for Akhmat's withdrawal==