The Gustav Line was a series of German military fortifications in Italy, constructed during World War II by Organisation Todt. They which ran from just north of where the Garigliano River flows into the Tyrrhenian Sea, to the mouth of the Sangro River on the Adriatic Sea.
The Allies had initially landed in the South of Italy and intended to progress Northwards, with the objective of captuing Rome. The strength of the Gustav line, combined with the mountaineous terrain and the tenacity of the German defenders resulted in the Allied forces being held up for a long time. Operation Shingle (the Anzio landings) were an attampt to outflank the defenses. The best-known battle on the Gustav Line was the Battle of Monte Cassino, at which the line was finally broken.
Following the crossing of the Garigliano, on January 17, 1944, by the British X Corps, Generalfeldmarschall Kesselring reinforced the Gustav Line with the 29th and 90th Panzergrenadier divisions (which had been in Rome). At the time of Operation Shingle (the landings at Anzio in 1944), the Gustav Line was commanded by General Heinrich von Vietinghoff of the 10th Armee.