Short answers, pulled from the story.
The first assault began on the 17th of January 1944, and the final Allied victory occurred on the 18th of May 1944. The German Senger Line collapsed on the 25th of May 1944 following the capture of the town.
Allied bombers dropped 1,400 tonnes of high explosives on the abbey on the 15th of February 1944 to reduce it to rubble. Major General Francis Tuker ordered the bombing because he concluded that smaller bombs were useless against the fortified position.
Monks decided to leave their ruined home at 07:30 on the 17th of February after the bombing destroyed the site. Two officers from the Hermann Göring Panzer Division had removed treasures to the Vatican ahead of the front in November 1943 to save the monastic community.
A total of 2,026 civilians were killed during the raids and the battle out of a prewar population of 20,000. The only people confirmed killed by the bombing of the monastery itself were 230 Italian civilians seeking refuge there.
The official position changed over a quarter-century to conclude in 1969 that the abbey was actually unoccupied by German troops before the bombing. This conclusion contradicted earlier Allied claims that the enemy used the abbey as an observation post.