II Corps XIV Panzer Corps Invasion of Italy Winter Line Gothic Line 1945 Spring Offensive The Battle of San Pietro Infine (commonly referred to as the "Battle of San Pietro") was a major engagement from 8–17 December 1943, in the Italian Campaign of World War II involving Allied forces attacking from the south against heavily fortified positions of the German "Winter Line" in and around the town of San Pietro Infine, just south of Monte Cassino about halfway between Naples and Rome.

The battle is also remembered as the first in which the troops of the Royal Italian Army (Regio Esercito) fought as co-belligerents of the Allies following the armistice with Italy.

Lieutenant General Bernard Montgomery's British Eighth Army advanced from the east following the Second Battle of El Alamein and the British-American invasion of French North Africa by Lieutenant General Kenneth Anderson's British First Army in Operation Torch had led to the surrender of almost 250,000 Axis forces in North Africa in May 1943.

Although the Allied powers were victorious, the Axis managed to evacuate over 100,000 men and 10,000 vehicles from Sicily across the Straits of Messina during the first seventeen days in August.

On 8 September, before the main invasion at Salerno by American Lieutenant General Mark W. Clark's Fifth Army (which contained significant British units), the surrender of Italy to the Allies was announced.

The invasion at Salerno was ultimately successful, although the Allies sustained heavy casualties, and subsequently captured nearby Naples on 1 October.

The German Commander-in-Chief (C-in-C) Albert Kesselring—had marked out the Winter Line as three parallel defensive systems to the south of Rome.

The Battle of San Pietro was preceded by Allied attacks on the Camino hill mass at the entrance to the Mignano Gap (named for the small town on the road at that point).

The direct attack on the German positions in and around San Pietro began on 8 December by Major General Geoffrey Keyes' II Corps of the Fifth Army.

The Germans counterattacked on 16 December to cover their withdrawal as they retreated to positions farther north at Cedro Hill, Monte Porchia, San Vittore, and the western spurs of Sambúcaro.

[9][10] By mid-January, Fifth Army had reached the formidable Gustav Line defenses and commenced the first Battle of Monte Cassino, which started on 17 January 1944.