Why Gryffindors and Slytherins Hate Each Other: A Marauder's Folktale

When Harry went to school, you couldn't enter a House's Common Room that wasn't your own, But once this was not the case. In fact, for the longest time Gryffindors could enter their Hufflepuff friends dormitories! It had been that way since the founder's era! But only recently, in the Marauder's Era did the no inter-house-mingling rule came into play. Here's why! Please review!