Short answers, pulled from the story.
The Gothic Line was a German and Italian defensive line built during the Italian Campaign of World War II. It formed Field Marshal Albert Kesselring's last major line of defense along the summits of the northern Apennine Mountains, facing the Allied Armies in Italy under General Sir Harold Alexander.
Hitler feared the Allies would use amphibious landings to outflank the Gothic Line's defenses and wanted to downgrade its importance in the eyes of both friend and foe. Kesselring renamed it the Green Line, or Grune Linie, in June 1944.
The Gothic Line was initially breached during Operation Olive in 1944, though Kesselring's forces kept retiring in good order. The line held with no decisive breakthrough until April 1945, during the final Allied offensive of the Italian Campaign.
General Sir Harold Alexander commanded the Allied Armies in Italy, with the British Eighth Army led first by Lieutenant-General Oliver Leese and later by Lieutenant-General Richard McCreery, and the U.S. Fifth Army led by Lieutenant General Mark W. Clark. Field Marshal Albert Kesselring commanded the opposing German forces.
Over 1,200,000 men took part in Operation Olive, described as the biggest battle of materiel ever fought in Italy. It pitted the British Eighth Army and U.S. Fifth Army against the German 10th and 14th Armies.
More than 15,000 slave labourers built over 2,000 fortified positions along the Gothic Line, including machine gun nests, casemates, bunkers, observation posts and artillery emplacements. The Tenth Army's sector alone held 72,517 Teller antitank mines and 23,172 S-mines by the end of August 1944.