The 'Mius-Linie' was a German well-sited and strongly fortified defensive line on the western bank of the Mius river in the southern USSR (December 1941/31 August 1943).

Soviet forces attempted to break through the 'Mius-Linie' during the course of two campaigns (between December 1941 and July 1942, and between February and August 1943) before succeeding at the end of the latter during the 'Donbass Offensive Operation' as the forces of the South Front broke through the German line in the area of ​​the village of Kuybyshevo. According to some accounts, the Soviet losses along the 'Mius-Linie' totalled something in the order of 150,000 men killed, missing, taken prisoner, wounded and taken ill.

For most of its length, the 100-mile (260-km) Mius river flows essentially south to debouch into the Sea of Azov in the area to the north-west of Taganrog. The Germans first reached the river in November 1941 during the later stages of 'Barbarossa', when forces of Generalfeldmarschall Gerd von Rundstedt’s Heeresgruppe 'Süd' crosse it and advanced eastward to Rostov-na-Donu. Driven back from this city on 29 November 1941 at the end of the Soviet forces' 'Rostov-na-Donu Defensive Operation', the Germans fell back to the line of the Mius river, which they deemed an excellent defensive position. The work on creating this defensive line was undertaken largely by Generaloberst Ewald von Kleist’s 1^st Panzerarmee.

The depth of the fortifications was in some places 6.85 miles (11 km), and the line extended from the coast northward long the western side of the Mius river, which had a taller =bank than the eastern side and thus allowed straightforward German observation of any build-up of Soviet forces. The defences incorporated the many cliffs, heights, ravines and rocky outcrops typical of this sector of the 'Donetsk ridge'. Most especially, the German defences were part of the Saur-Mogila mound, a 912-ft (278-m) height close to Saurovka in the mining area of the Donetsk region.

Some 800 settlements were incorporated into the defences in a forward strip some 28 to 31 miles (45 to 50 km) wide. The second defence line extended along the western banks of the Krynka and Mokry Elanchik rivers and through the settlements of Krasny Kut, Manuylovka and Andreyevka . The third defence line extended along the western bank of the Kalmius River, east of Stalino, Makeyevka and Gorlovka, and never became embroiled in the area’s fighting.

For the construction of the mass of the line’s fortifications, rails and large quantities of timber were used, much of the local housing stock was dismantled. The construction of the defensive line was undertaken largely by impressed local civilians, who included women, children and the elderly. Chains of pillboxes and bunkers, machine gun nests and artillery positions were built. Fields were mined, trenches dug, and anti-tank ditches and barbed wire entanglements were established. The depth of the minefields was at least 220 yards (200 m), and the density of pillboxes and bunkers was in the order of 20 to 30 per km².

The German forces had crossed the Mius river toward the east in the middle of October 1941, and von Kleist’s 1^st Panzergruppe (redesigned as the 1^st Panzerarmee on 25 October) and took Taganrog on 17 October. The onset of the autumn thaw and its attendant rasputitsa mud then combined with the exhaustion of their fuel supplies forced the Germans to delay farther exploitation to the east. von Rundstedt believed that the offensive should not be continued on the eve of winter, and this triggered the decision to embark on the construction of a line of fortifications along the Mius river. However, Adolf Hitler insisted that the offensive be continued, and on 17 November von Kleist’s armour reached Rostov-na-Don. After a week of stubborn fighting, the Soviet defence of the city was broken, and on the night of 19/20 November German troops entered this strategically important city 20 miles (32 km) upstream of the mouth of the conjoined Don and Donets rivers on the Sea of Azov.

As von Rundstedt had predicted, the Germans could not hold the city, and on 28 November 28, Soviet forces commanded by Marshal Sovetskogo Soyuza Semyon K. Timoshenko retook the city in bloody fighting. von Rundstedt requested but was refused Hitler’s permission to withdraw his troops to the prepared line of defences on the Mius river. Nevertheless, the order to withdraw was given, for which von Rundstedt was removed from command on the same day. The army group’s new commander was Generalfeldmarschall Walter von Reichenau, and on his arrival he confirmed the order to retreat. The 'Mius-Linie' was then held by units of Generaloberst Hermann Hoth’s (from 20 April 1942 General Hans von Salmuth’s) 17^th Army throughout the spring of the 1942 until the start of the 'Blau' offensive into the Caucasus.

The German defence on the 'Mius-Linie' continued until July 1942 when, after the failure of the Soviet offensive near Kharkov, the Germans launched their 'Edelweiss' offensive into the Kuban and the Caucasus areas. On 24 July, elements of the 17^th Army entered Rostov-na-Donu once again. This time, the Soviet troops were unable to retake the city.

After the encirclement of Generaloberst Friedrich Paulus’s 6^th Army at Stalingrad in December 1942, Generalfeldmarschall Wilhelm List’s Heeresgruppe 'A' in the Kuban and the northern Caucasus was threatened with encirclement as the Soviet forces in the Stalingrad region were much closer than the German forces in the Caucasus to Rostov-na-Donu, through which passed the group’s communication with the rest of the German strength on the Eastern Front.

Hitler’s order to retreat from the Caucasus followed on 27 December 1942, when the Soviet forces were already dangerously close to Rostov-na-Donu. Stubborn fighting on the outskirts of the city continued throughout January 1943, and the Germans nevertheless managed to hold back the Soviet onslaught: the 1^st Panzerarmee crossed the Don river to the west and thereby escaped encirclement. The last German troops left Rostov-na-Donu, which the Soviets liberated on 14 February 1943, and once again fell back to the 'Mius-Linie', ion which they established themselves until the summer of 1943.

Soviet preparations for the breakthrough of the 'Mius-Linie' began in May 1943, and the first but unsuccessful Soviet attempt on the line was the 'Donbas Strategic Offensive Operation', which lasted from 17 July to 2 August 1943.

The second Soviet offensive was the 'Mius-Mariupol Offensive Operation' which was the second half of the '2^nd Donbas Strategic Offensive Operation', which began on 18 August 1943 and ended when formations and units of the South Front finally broke through near the village of Kuybyshevo and the Soviets pressed through and started to expand their efforts to the west.