Battle of San Pietro Infine 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 eventual Allied victory in the battle was crucial in the ultimate drive to the north to liberate Rome . The battle is also remembered as the first in which the troops of the Italian Royal Army ( " Regio Esercito " ) fought as co - belligerents of the Allies following the armistice with Italy . The original town of San Pietro Infine was destroyed in the battle ; the modern , rebuilt town of the same name is located a few hundred meters away . Background . North Africa and Sicily . The Allied invasion of Italy from the south followed the Allied successes in North Africa . Eighth Army ' s advance from the east following the Second Battle of El Alamein and the British - American invasion of French North Africa by the British First Army in Operation Torch had led by May 1943 to the surrender of Axis forces in Africa . The Germans retreated to the island of Sicily and on the night of 9 / 10 July 1943 , an Allied armada of 2 , 590 vessels launched one of the largest combined operations of World War II : the invasion of Sicily . Over the next five weeks , 500 , 000 Allied soldiers , sailors , and airmen fought German and Italian forces for control of the island . 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 . The Allies then invaded the Italian mainland in September 1943 at Salerno , in Calabria ( " Operation Baytown " ) and Taranto ( " Operation Slapstick " ) . On 8 September , before the main invasion , the surrender of Italy to the Allies was announced . Italian units ceased combat , and the Italian Navy sailed to Allied ports to surrender . This changed the German defensive strategy greatly , and the Germans now regarded their former allies as enemies and moved to disarm Italian units and occupy important defensive positions . The invasion at Salerno was ultimately successful and Allied forces took nearby Naples on 1 October . German forces then withdrew to the north toward Rome and dug in along a series of well - fortified lines . By late 1943 fighting had reached the Winter Line . Italy . The German commander — General Albert Kesselring — had marked out the " Winter Line " as three parallel defensive systems to the south of Rome . The defensives lines were called the Reinhard Line , Gustav Line and Hitler Line , placed one from the other , taking advantage of the point at which the Italian Peninsula is narrowest ; they served as a formidable series of obstacles in the path of the Allied march toward Rome . The Reinhard was the southernmost of the three and was the German fall - back position from the Barbara Line and Volturno Line further to the south as German forces retreated gradually up the peninsula . ( The Reinhard was also called the Bernhardt Line . ) The Reinhard was actually a southern bulge in the stronger Gustav line to the north . On the eastern side , the Reinhard went from the Sangro River to the Adriatic Sea ( along which length it was identical to the Gustav Line ) ; then , in the west , it bulged south from Cassino to incorporate the mountains overlooking the approaches to the Liri Valley and then moved west to the mouth of the Garigliano River . The line passed directly through the town of San Pietro Infine , blocking the Mignano Gap , the pass through which Route 6 , the main road up the center of Italy from Naples to Rome , ran toward Cassino and the entrance to the Liri valley . Preparations . The Germans occupied San Pietro in September 1943 to prepare the defenses . They evacuated all non - essential Italians from the town , meaning women , children and old men ; they conscripted able - bodied men to help set up the defenses and requisitioned available vehicles and beasts of burden . They set up a defensive apparatus in the whole territory , in particular on Mount Sambúcaro and Mount Lungo , which overlooked the Mignano Gap . These were strategically important positions because they allowed the control of the long stretch of Route 6 , important for the advance of the Allies . The Fifth Army began to attack the Reinhard / Bernhardt Line on 5 November , and the attacks continued into December . 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 entire hill mass is about long and wide . After that , the main Allied effort was against the German defenses on Mount Sambùcaro and Mount Lungo , which dominated the narrow valley on the east and west respectively . As a point of historical interest , the assault on Mount Lungo was aided for the first time by the 1st Italian Motorized Group , part of the recently reconstituted Italian army , now fighting on the side of the Allies . The battle . The direct attack on the German positions in and around San Pietro began on 8 December by II Corps of the Fifth Army . The positions were defended by the second and third battalions of the 15th " Panzer " Grenadier Regiment and the second battalion of the 71st Panzer Grenadier Regiment , all part of German Tenth Army ' s XIV Panzer Corps . After a week of intense attacks and counter - attacks , the U . S . 36th Division ' s 143rd Infantry Regiment and the 82nd Airborne Division ' s 504th Parachute Infantry Regiment commanded the heights of the Sambùcaro mass . The U . S . 36th Division , then planned a further effort for 15 December . 143rd Infantry assisted by 504th PIR would continue to push west along the shoulders of Sambùcaro and take San Vittore del Lazio while to the south of Route 6 142nd Infantry Regiment supported by the Italian 1st Motorized Group were to capture Mount Lungo . In the center , 141st Infantry would attack San Pietro itself . The main attack of the 36th Division started at 12 : 00 on 15 December . In an effort to break the German defenses in the town , two platoons from the 753rd Tank Battalion attacked with 16 Sherman Tank and Tank Destroyers . The armored attack failed due to mines and anti - tank fire . Four of the 16 tanks survived . After four successive Allied attacks and German counter - attacks , the Germans pulled back from San Pietro since the dominating ground on both flanks , Mount Lungo and the Sambùcaro peaks , was now in II Corps ' possession . The Germans launched a counter - attack on 16 December to cover their withdrawal as they retreated to positions farther north at Cedro Hill , Mount Porchia , San Vittore , and the western spurs of Sambúcaro . Aftermath . The Battle of San Pietro was part of the overall campaign to breach the Bernhardt / Reinhard Line , some deep at that point . It took six weeks of heavy fighting — from early November to late December — to overcome the German defenses . During that time , the Fifth Army sustained 16 , 000 casualties . The highway through the Mignano Gap to the Liri Valley was nicknamed " Death Valley " by members of the attacking force . The battle destroyed the town of San Pietro Infine completely . Destruction was wrought by a combination of close combat , both Allied and German mortar and artillery , and German " scorched earth " policy . Both the battle and the plight of the civilian population have inspired numerous accounts , most famous of which is the John Huston film " The Battle of San Pietro " . 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 .