 Complete the following phrase:  The Winter Line proved a major obstacle to the Allies at the end of 1943, halting the Fifth Armys advance on the western side of Italy. Although the Gustav Line was penetrated on the Eighth Armys Adriatic front, and Ortona was liberated with heavy casualties to Canadian troops, the blizzards, drifting snow and zero visibility at the end of December caused the advance to grind to a halt. The Allies focus then turned to the western front, where an attack through the Liri valley was considered to have the best chance of a breakthrough towards the Italian capital. Landings behind the line 