Crowley didn't like Rome.
It wasn't like the old days. Babylon had been wonderful, Egypt had been a very nice holiday spot (except for that bit with the locusts), and even Greece had been nice. That Socrates fellow was always ready to sit down and have a drink and ask Crowley questions to which Crowley would readily give answers that always made Socrates ask even more annoying questions to passers by.
You didn't get many people like that in Rome.
The most amusing couple of years had been when Caligula was in charge; it was always good for a laugh to see his horse in the Senate. But that time had come and gone, and then the Romans started doing uncomfortable things like persecuting Christians, and Crowley spent a lot of time getting drunk and staying away from the coliseums and wondering if his people had anything to do with the whole mess or whether it was an entirely human thing to do and exactly why lions were involved.
Also, the Enemy was hanging around.
In fact, the Enemy was hanging around in the same parts of the city as Crowley. This was probably because the angel didn't like watching Christians killed for sport any more than Crowley did, but the demon indulged in the idea that Aziraphale was hanging around just to get him annoyed.
Not that annoying people was a very angelic thing to do, but Crowley could still vividly remember the time when he'd had to rescue the angel from an angry mob and a couple of discuses after Aziraphale had attempted converting the populace of Athens to monotheism. They just weren't ready for the idea of only one god, Crowley had explained to the angel. Then he'd realized that he was being perfectly civil to the Enemy, and had quickly wandered off to tempt some people.
The fact still remained that Crowley was getting used to the only face he'd seen consistently for the last four thousand years or so, and that was even more annoying than knowing that Aziraphale was in Rome. It just wasn't properly demonic, enjoying the company of an angel.
At the moment, Crowley was sitting in a tavern, looking suspiciously at a mug of something that claimed to be perfectly good wine, and he was doing his best to ignore the fact that a certain angel had just waltzed in the door.
"Crowley!" Aziraphale said enthusiastically, sitting down across the table from the demon and beaming at him.
"Hi," Crowley said, and slid the mug he had been scrutinizing across the table. "Does this look like actual wine to you?"
Aziraphale blinked at it and slid it back across the table. "Now it does," he said, looking pleased.
"Thanks," Crowley mumbled.
"My pleasure, dear boy." The angel leaned back in his chair and smiled benignly around the tavern. "Lovely day, isn't it?"
"I'm sure," Crowley said, tentatively sipping from the mug and finding with surprise that the angel seemed to actually have good taste in drink. "Anything making the day particularly lovely?" Aziraphale looked so annoyingly happy that he added, "Screams from the coliseum music to your ears, eh?"
"The blood of the martyrs is the seed of the Church," the angel replied stiffly.
Crowley made a noncommittal noise and drained his mug.
"Although," Aziraphale added, "that is rather relevant. The Church, I mean. Martyrs. Er." He rummaged around in a silly-looking satchel and eventually produced a piece of parchment. "I'd like you to look at this."
"What is it?" Crowley asked, intrigued in spite of himself.
Aziraphale pushed the parchment across the table, and as Crowley scanned it, he explained, "I've met this wonderful fellow by the name of Dennis the Short, and he's decided to bring things a bit more up-to-date, give important things the importance they deserve, you know -- and obviously the birth of the Savior is a bit more important than the founding of Rome --"
"'BC'," Crowley read. "Stand for something?"
"Oh yes," Aziraphale smiled, "that's 'Before Christ', you see. And the AD's 'Anno Domini'."
"I'm not sure this'll catch on, angel."
"Come now, more people hear the Word every day. They're writing the whole thing down. One day you'll wake up, and the whole Empire will be going to Church on Sunday, just you wait."
Crowley snorted in what he hoped sounded like disbelief. "Don't hold your breath." He felt a little better when he saw a puzzled expression creep embarrassedly across the angel's face. It was always nice to know you were up with the current slang and Heaven wasn't. Outdated, the lot of them.
Except that they were inventing a new dating system.
Crowley glared at the innocent parchment before him. In Aziraphale's copperplate handwriting, somewhere vaguely between 200 AD and 300 AD, were the neat words you are here. Crowley's eyes traveled back along the timeline, to where the angel's writing claimed the end of Augustus Caesar's reign to be in 14 AD. Crowley did the necessary calculation in his head, and began to grin.
"Aziraphale," he said, "I never knew Mary gave birth to a five-year-old."
The angel blinked at him. "What?"
"According to this," Crowley said, tapping the parchment with a pale finger, "Jesus was born in the year one. Also according to this, Augustus got it in the year fourteen. But our precious messiah was nineteen with Augustus got kicked out of the top seat. I remember that. He'd just started to be really annoying over in Nazareth, and then things got messy in Rome. Timeline's wrong, angel."
"Oh. Oh dear," said Aziraphale. "Are you sure? Dear me. Dennis did all the calculations."
"Our Short friend wasn't alive then," Crowley pointed out. "Also, I wouldn't put too much stock in his calculations. Idiotic Western civilizations don't know how to count right anyway. Ever been to Arabia, Aziraphale?"
"What?" the angel said, thrown.
Crowley was on a roll. "Clever buggers, the Arabs. They know about zero. This timeline, here -- one BC, Herod does some nasty stuff. One AD, Jesus is born and a choir of angels act flashy." Crowley paused for a moment, trying to work out why it said the bit about the angels, before shrugging and concluding, "So we've got one BC, and one AD, but no, you know, zero BC for Herod to do nasty stuff in, or a -- a zero AD for Jesus to be born in. Numbers can't just disappear."
"But zero means nothing, doesn't it?" Aziraphale frowned. "There can't be a year nothing."
Crowley took another gulp from his mug, which realized with surprise that it was not in fact as empty as it had thought. "Still not accurate," the demon said. "And it still says that Jesus was born as a five-year-old."
Aziraphale sighed. "I'll take that up with Dennis." He looked edgewise at Crowley. "Other than that, does it look all right?"
"Yeah," Crowley said, rolling his eyes. "Really excellent. A hundred years from now, everyone will be saying what a brilliant idea this was, and Up There will give you a commendation or something."
"Oh yes, I do hope so," said Aziraphale cheerfully. He was remarkably good at not recognizing sarcasm when he preferred to.
Crowley sighed and handed the parchment back to Aziraphale. "All these calculations are making my head ache. Can I tempt you to a drink?"
The angel slipped his parchment back inside the satchel and agreed that yes, Crowley could indeed do that.
So they spent the afternoon drinking and arguing vaguely about lions, and Crowley hoped that Aziraphale was sufficiently distracted to forget about his silly timeline. Not because, you know, Christian ideas weren't wildly popular and parading the timeline around was liable to get Aziraphale killed – er, temporarily disembodied. No, because Aziraphale was the Enemy and getting him disembodied for a while would be a good thing. It would just be nice if the timeline disappeared because then Crowley wouldn't have to go memorizing a new set of dates to keep track of.
Besides, it would never catch on.
1. Not really waltzed. The waltz hadn't been invented yet, and even when it was Aziraphale didn't bother to learn it.
2. Or Dionysius Exiguus, for anyone wanting to call him by a less ridiculous, less pronounceable, and more Latin name.
3. Unfortunately, although Aziraphale had remembered one of the essentials for anyone orienting themselves in a foreign place or time, he had forgotten the invaluable map that shows you where the toilets are.
4. More technically, a convenient thing. Demons, by nature, are not supposed to like good things. And Crowley definitely wasn't an exception or anything.