Nazi stronghold at Monte Cassino abbey an obstacle for Allied troops in World War II

Monte Casino, with its Benedictine monastery, was a Nazi stronghold controlling Allied troop movements. The Allies suspected the monastery was used by Nazis for observation, directing shelling against American troops. To avoid damaging the historic site, American artillery targeted the hillside below the monastery.

Describe the challenges faced by the Allied troops in the vicinity of Monte Cassino.

What was the historical importance of the building mentioned in the text?