The defense line prepared along the Apennines was named by the Germans Gothic Line (Gotenstellung). During the Summer of 1944, when it was feared the Allied armies would easily breach it and fan out in the Po Valley after their advance North of Rome, the name was changed to Green Line (Grune Linie), so as not to compromise such an imposing denomination, but the first name survived in general parlance.
The tactics of retreating to organized lines of defense prepared along prominent terrain features up the Italian boot (such as the "Gustav Line" at Cassino) was successfully followed by the German Army throughout the Italian Campaign. The German command had started to study the idea of fortifying the Central Apennines already in August 1943, when the Allies were still fighting in Sicily. Work however started only during the Spring of 1944, under the direction of the Todt work organization.
The Gothic Line was not a continuous line of fortification, but rather a series of strong-points arranged in depth, exploiting the natural terrain features which favored the defender. Traversing the Italian mainland from the Tyrrenian coast North of Viareggio to the Adriatic at Pesaro, the line extended for more than 300 km. It included thousands of field fortifications made of wood, rock or steel-girded concrete, and included long antitank ditches such as the one at Santa Lucia near the Futa Pass. Extended minefields and wire emplacements completed the picture.
Luckily for the Allies, construction work was still incomplete when the advancing armies approached the Central Apennines. Both coastlines, being more vulnerable, had received priority and were better defended. Due to terrain features, the weakest points in the line were the Futa Pass and the Adriatic coast. These areas were therefore the most heavily defended. At the Futa Pass the Germans placed two of the five divisions defending the whole Apennines sector. Apart from the 5-km long antitank ditch, routes of attack were covered by concrete pillboxes and Panther tank turrets with 75 mm guns. The advance line of resistance was usually anchored on strong-points covered by extended wire and mine fields.
Because of the enemy disposition, the US command decided to attempt a breakthrough at the less defended Giogo Pass, feinting a covering attack in force against the Futa Pass by the 34th and 91st Ids. Allied operations along the Thyrrenian coast (the sector of the IV Army Corps) took on a secondary role to those in the Central Apennines North of Florence till the final offensive in the Spring of 1945.