An ancient Benedictine monastery overlooking the battleground was destroyed by bombers in February 1944.
But bad allied co-ordination before and after the attack allowed German forces to occupy the ruins.
In the photo above , New Zealand Troops fight hand-to-hand through the streets of the town.
The New York Times said the onslaught from bombers and artillery on 15 February 1944 was the worst ever directed at a single building.
But parts still remained standing.
The battle at Monte Cassino had begun a month earlier, as allied forces fought up through Italy.
It ended in May, with up to a quarter of a million dead or wounded.
The advance into Cassino was preceded by a massive aerial bombardment.
Hundreds of bombers dropped nearly 1,000 tons of high explosive - about five tons for every German soldier in the town.
But the resulting craters and piles of rubble hindered infantry movements, and blocked the path of allied tanks.
The monastery - what was left of it - was finally taken by Polish forces on 18 May.
A handful of wounded German soldiers were found sheltering in the crypt containing St Benedict's tomb.
Fragments of ancient frescoes and broken sculptures lay among unexploded shells and the bodies of dead soldiers.
The appalling conditions at Monte Cassino came as a shock even to hardened German troops transferred from the Eastern front.
Some German soldiers were poorly equipped and froze to death for lack of proper clothing.
The allied victory was achieved as much as anything by sheer weight of men and military hardware.
Today the monastery has been re-built.
It looks down over the new town of Cassino, the main road from Naples to Rome, and thousands of war graves.
In this cemetery lie Britons, New Zealanders, Canadians, Indians and Gurkhas.
Polish and German cemeteries lie not far away.
Acknowledgements to the bbc.co.uk for the information and photos used in this post
