After the Allied capture of the Italian capital of Rome on 4 June 1944 following the successful breakthrough at Monte Cassino and Anzio during Operation Diadem in May 1944, the German 14th and 10th Armies fell back: the 14th along the Tyrrhenian front and the 10th through central Italy and the Adriatic coast. The 10th escaped because General Mark W. Clark ordered Lucian Truscott to choose Operation Turtle towards Rome rather than Operation Buffalo as ordered by Sir Harold R. L. G. Alexander, which would have cut Route 6 at Valmonte. There was a huge gap between the armies and with the Allies advancing some 10 km per day, the flanks of both armies were exposed and encirclement was threatened.[1]
Between 4 June and 16 June, whilst maintaining contact with the advancing Allies, Kesselring executed a remarkable and unorthodox maneuver with his depleted divisions, resulting in his two armies aligning and uniting their wings on the defensive positions on the Trasimene Line.[1] Remarkable though this was, he was probably helped by the confusion caused in the Allied advance by the relieving of the U.S. II and VI Corps (substituted by Major General Willis D. Crittenberger's U.S. IV Corps and Lieutenant GeneralAlphonse Juin's French Expeditionary Corps). The British X Corps, under Lieutenant General Richard McCreery, had also been brought into the line on XIII Corps' right whilst V Corps had been relieved by the Polish II Corps, under Lieutenant General Władysław Anders.
The U.S. IV Corps also found progress slow but by 1 July had crossed the river Cecina and were within 20 miles (32 km) of Livorno. Meanwhile, the French Corps had been held up on the river Orcia west of Lake Trasimene until the parachutist defenders withdrew on 27 June allowing them to enter Siena on 3 July.[7]