ROME – From the outside, it’s often assumed that the fundamental division in the Vatican runs between friends and foes of Pope Francis. That’s a fallacy for two reasons: 1) Tensions around Francis’s reforms generally are more nuanced than outright support or opposition, and 2) Most people in the Vatican don’t really care about such matters anyway.

I guarantee you that the guy pumping gas at the Vatican’s filling station, or the lady giving you your greens in the Vatican grocery store, aren’t coming to work thinking about the pope’s latest motu proprio (unless it involves their salaries or pensions.)

There is, however, a genuine laceration in the Vatican just like all of Rome, unyielding and savage, where “nuance” never applies. Especially for those who hail from Rome itself, it grips everyone from cardinals to street sweepers, so totalizing in its embrace that it’s passed down through the generations, and where hate for the enemy is almost as strong as love for one’s own.

I’m talking about the chasm between Laziali and Romanisti, meaning fans of the two great professional soccer teams in the city of Rome. (In the interests of full disclosure, the Allens are Romanisti. I’m writing this column beneath my team flag that reads, “La Roma non si discute, si ama, which means, “You don’t discuss Roma, you love her.”)

To understand how bitter the rivalry is, we should begin by noting that soccer – calcio, to use the Italian word – is a civil religion here. America is sports-crazy too, but our passions are divided among football, basketball, baseball, hockey, mixed martial arts, stock car racing, etc. In Italy there’s really only calcio, and it’s all-consuming.

When it comes to the city of Rome, it’s also useful to remember that its founding myth pivots on a fratricide, Romulus killing Remus. Over the centuries, brother v. brother always has been a defining streak of Roman life. Nowhere is that more evident than during the pair of occasions each year when the two brother squads of Rome face one another on the field of battle.

Tonight at 6:00 p.m. Rome time brings the latest Roma-Lazio “derby,” what the Italians call a soccer game between cross-town rivals. It’s a dead-lock certainty that a far greater share of Vatican personnel will be glued to their television sets for those two hours than, say, those who followed any portion of the live feed of the pope’s recent outing to Hungary and Slovakia. A fair number probably will be late to work Monday, since they’ll have trekked out to Rome’s Olympic Stadium to take part in an annual ritual that’s as invested with sacred meaning as any Catholic liturgy.

Both teams come into tonight’s game in accustomed positions, looking competitive but not elite. Roma started strong this year under its new coach, the legendary Jose Mourinho, winning its first six games handily, but has struggled over the last two. Lazio, meanwhile, has either tied or lost its last four games after thumping bottom dweller Spezia 6-1 in late August.

Indeed, the fact that neither Roma nor Lazio are routinely among the big winners in Italian soccer is another factor in making their rivalry so bitter. Lazio last won the scudetto, the Italian championship, in 2000, Roma in 2001, so both are twenty years removed from glory. The Turin-based Juventus has more hardware by itself than Roma and Lazio combined, so the fact they don’t win much else makes beating each other, by default, the litmus test of a successful year.

When an outsider arrives in the Vatican, no matter what office they hold, they face a basic choice: Stay out of the Roma/Lazio divide, or become a true local and take sides. (In that regard, Portuguese Cardinal José Saraiva Martins has always been something of a living miracle. When he got to Rome in the late 1980s he became a Lazio fan, but he’s such a nice guy even diehard Romanisti adopted him too.)

Pope Francis famously is a fan of San Lorenzo in his native Argentina, and he’s never stated any rooting interesting in the rivalry that defines his adopted city. That hasn’t stopped Romans from attempting to claim him, however. Laziali have long believed Francis is one of them, based on the fact that when he was a young Jesuit philosophy teacher in Santa Fè, Argentina, in the 1960s, his housekeeper was the sister of the wife of the grandfather of Lucas Martin Castroman, an Argentine soccer player who scored a celebrated goal for Lazio in the 2001 derby at the very last minute to deny Roma victory.

Yes, you read that right – Lazio’s claim on the pope rests on a housekeeper he knew briefly fifty years ago being the sister of the wife of somebody’s grandfather. Such is the logic of a rivalry.

In the abstract, you might expect Francis to incline to Roma, given the historic sociology of the two teams. Lazio was founded in 1900 as an homage to Rome’s imperial past, adopting the eagle as its symbol and the regal colors of white and sky blue, and it appealed to the high middle class and social elites. Roma was launched in 1927 using the popular city colors of red and gold, it adopted the wolf of the Romulus and Remus myth as its mascot, and it appealed to the lower classes and the streets. Politically, Lazio was associated with the establishment, Roma with the radicals, populists and communists, i.e., the rabble.

Today, such distinctions largely have vanished, so you’ll find Roma fans selling high-end real estate and Lazio fans peddling smokes – I can personally testify to both, from our own neighborhood. Yet the muscle memory of those old antagonisms endures, adding yet more intensity to the rivalry.

In that sense, the Roma/Lazio contest actually may be ideally suited for the Vatican, since the antagonists are fighting in part over things neither side has ever experienced, just like today’s generation of 30-year-old clerics splitting hairs over Vatican II.

So, if you need something from the Vatican right now, here’s my advice.

Find out if the official you’re dealing with is a Romanista or a Laziale, then check the scores for Italian soccer before you go to bed. If your contact’s team loses, stay away for a while, because he or she will be trapped existentially in the pit of despair from “Princess Bride” and in no mood to be helpful.

If the right team wins, on the other hand, strike now, because I promise you won’t find him or her in a more benevolent humor all year.

Forza Roma!

Follow John Allen on Twitter: @JohnLAllenJr