It was late at night in the Easter holidays when they thought of the idea. Peter lay on a camp bed on the floor, James was in his own bed, and Sirius was enjoying the company of Remus in his bed with him. They were all lying comfortably, the blanket half off James, Peter covered up to his chin in his own blankets and Sirius lying comfortably on Remus' chest, Remus playing absentmindedly with Sirius' hair.
"We need to make something. Something useful but awesome as well." James said into the quiet room. "Like a map or something?" Peter asked. "Come on Pete, when was the last time someone walking around with a map looked cool." Sirius said. "No, I think Wormtail's onto something. What if it was a map of Hogwarts, with all the rooms and hidden passages." Remus suggested. "Yeah and you could see people moving around, you'd never have to worry about looking for someone, you could just see their name on the map." James added. "Ok, not going to lie, but that sounds wicked." Sirius said. "Exactly, let's start making it." Remus said.
From that night on they worked hard, making measurements and scaling the castle. Once they had a map of the castle James cast a few powerful spells so that the dots of students and teachers appeared. With a few more muttered words and flicks of his wand, James made the people move. The four sixth year Gryffindor boys watched in amazement as they saw Dumbledore's footprints pace around his study.
"We need to sign it." Sirius said. "We need to name it." James said. "Well that's easy, the Marauders Map." Sirius replied. "Let's write our nicknames on it." Remus suggested. "Wait a minute, we don't want just anybody to see this. We need a password or something." James said. "Yeah, you could say something and tap it with your wand, and then the map appears." Sirius said. "But what should the words be?" Remus asked. Silently, Peter lifted his shirt, to reveal the words 'I solemnly swear I'm up to no good.' "Yes!" James shouted, hugging Peter. "And mischief managed to lock it again." Sirius said.
"Who's name should go first?" Remus asked. "Mine of course, I'm clearly the most handsome of this group." James said. "No way James, my nickname is way better than yours, and are you saying you're more handsome than me? Because that's not possible." Sirius said, standing up. "See here Sirius, we want people to know that mature people made this map, not people who pretend to be more handsome than the person who is clearly more handsome." James replied. "Shut up!" Remus shouted, James and Sirius glared at him. "I'm going first because I made about eighty percent of this map, and then Pete, because he's the only one who hasn't pissed me off, then Sirius because what sort of a boyfriend would I be if I put him last, then James so that your name is the one that stays on the tongue." Remus said. "Fine." James and Sirius said at the same time.
With that the map was complete. Messes Moony, Wormtail, Padfoot and Prongs looked down happily at their accomplishment.