Roman Empire lasted 500yr. .... the process of "decline" was long and painful , they tried everything in vain.... there are MANY reasons why Roman Empire collapsed and up to today historians are divided WHICH REASON WAS THE MOST CRUCIAL .... I give a few out of the many reasons: 1 - the main source of grain used to come from North Africa and when this land was conquered by barbarians - grain supply stopped 2 - decline of moral values of people in power ..... there are at least 10 important reasons I can give...