As legend goes, at the height of the Roman Empire a citizen could walk across the Earth unharmed, cloaked only in the protection of the words civis Romanus — I am a Roman citizen. So great was the retribution of Rome, universally understood as certain, should any harm befall even one of its citizens.

It took several centuries, but even the Roman Empire fell from a combination of economic and social problems along with barbaric force from the outside. And while Saturday in Tuscaloosa featured only a single football game, it could well spell the eventual doom of an empire that has ruled college football.

The Alabama Crimson Tide entered this weekend as the kings and emperors — not only of the SEC but of all of college football — with all the crystal and gold to prove it. LSU entered this weekend as the upstart invaders, with a smirking senior QB and a sneaky-good defense.

Once it was all over Saturday night, once President Trump’s motorcade was far and gone, the empire that was Alabama football could well be inching toward decline: first in a hailstorm of fumbles of penalties, and late in a lack of defensive stops and so many Tiger roars.

Add it up and it is a 46-41 LSU victory that gives the Tigers the inside track to the SEC title game and College Football Playoff and leaves a gigantic uphill climb for Alabama to get back into the national-title picture.

It wasn’t so much that No. 1 LSU won, as rare is the team in history that wins all its games in a single season. Even in Nick Saban’s decade of dominance, Alabama has precisely one perfect season — the initial NC team of 2009 went 14-0.

But it was the manner in which the Tigers — who had lost 8 straight to the Tide coming in — punched No. 2 Alabama in the mouth early and kept on swinging in the late rounds that was surprising.

LSU QB Joe Burrow was laser-sharp all day long, throwing for 393 yards and 3 TDs. The Tigers blitzed and confused Tide QB Tua Tagovailoa with stunning regularity. LSU ran the ball effectively when it wanted, and Alabama was stuffed on the ground when it needed a yard.

One could even make a legitimate claim that Ed Orgeron — who infamously growled “We comin'” at reporters after being embarrassed in Tuscaloosa 2 years ago — outcoached Saban when it mattered the most.

If LSU’s victory over Alabama looked familiar, it is for good reason. Clemson wrote this exact Tide-whipping script in last year’s national title game: harass Tagovailoa into mistakes and frustrate the Tide defense with a pinpoint passing attack. While the final score wasn’t as lopsided as that Clemson barrage left behind, the point was still made.

And when Alabama made it a game in the 4th quarter, twice pulling to within a score, LSU answered with the kind of authority that wins national championships.

Twice it was running back Clyde Edwards-Helaire with 4th-quarter TD runs to finish long drives headed straight into Alabama’s raucous student section.

Twice it was the Tigers dancing on the visiting sidelines.

Twice it was Alabama scratching its head trying to solve the Rubik’s Cube that is LSU’s offense.

And even when DeVonta Smith somehow got behind the LSU secondary for an 85-yard TD reception to give the Tide one last gasp of hope in the final 90 seconds, it was the Tigers who pounced on a well-executed onside kick and then picked up a 1st down to seal the deal.

In the early going, Alabama gave little hope to the 101,000-plus who endured super-long Secret Service lines to pile into Bryant-Denny Stadium hope they would see anything other than a blowout.

Alabama fumbled twice and committed a costly penalty within the game’s first 10 minutes to put itself in a huge early hole. Tagovailoa — who had arthroscopic “tightrope” surgery on his right ankle just 21 days before — fumbled without being touched inside the 10 on the Tide’s 1st possession to cough up the chance to get at least 3 points.

After LSU marched 92 yards on just 6 plays to strike first, Alabama sputtered at midfield and punted … or at least tried to. Ty Perine, the Tide’s third punter of the season, fumbled a clean snap and was snowed under by the Tigers’ defense.

From there, Burrow appeared to give it right back — as Alabama’s Trevon Diggs picked Burrow off at the Tide 20. But Alabama ran a 12th player on the field right before the ball was snapped — a penalty that negated a turnover and ultimately cost Alabama 3 more points.

Alabama’s defense, vaunted for a decade-plus for keeping even the most average of Tide offenses in championship contention, looked like a Pop Warner squad during a particularly potent LSU drive early in the 2nd quarter. Burrow and the Tigers matriculated 75 yards on the Tide — highlighted by not 1 but 2 Alabama defensive backs blowing coverage on Terrace Marshall en route to a 29-yard TD catch.

Even when Alabama did something unmistakably right, the Tide managed to shoot itself in the foot. Smith beat his man at the line of scrimmage en route to catching a 64-yard TD dart from Tagovailoa … only to then see kicker Joseph Bulovas whiff an extra point that would have brought Alabama to within 2 points midway through the 2nd quarter.

LSU then capitalized on a controversial call when Thaddeus Moss stepped out of bounds before catching a ball near the goal line. Officials ruled he was pushed out and re-established position, and the ensuing LSU touchdown made it 26-13.

Tagovailoa then needed precisely 2 plays to uncork his 3rd interception of the season after the LSU score, throwing into double coverage and Patrick Queen jumping the route with 11 seconds remaining in the half. Burrow needed only 5 seconds to dagger the Tide secondary, as Edwards-Helaire hauled in a 13-yarder for a 20-point lead.

Burrow finished the 1st half with more touchdowns (3) than incompletions (2, on 18-of-20 passing for 252 yards) and armfuls of Heisman Trophy ballots that seemingly were locked to Tagovailoa when the season began.

More miscues followed in the 2nd half. Tide WR Jerry Jeudy, who was money in the game’s first 30 minutes, dropped a sure TD bomb in the 3rd quarter. Burrow escaped again and again to change sure sacks into scrambling completions.

From there, the game turned into a thrilling, end-to-end 100-meter dash that always felt like LSU had a 5-yard head start on.

Where Alabama goes from here is anyone’s guess.

The traditional media and coaching pollsters will have to decide if a 1-loss Crimson Tide is better than, say, an undefeated Minnesota team that spanked No. 4 Penn State on Saturday. Or if a 1-loss Crimson Tide is better than, say, an undefeated Baylor team that survived TCU. Or if a 1-loss Crimson Tide team is better than a 1-loss Georgia team — which at No. 6 was the next-best SEC squad in the rankings heading into Saturday.

Or will Alabama Fatigue finally catch up with the Tide, which has been in all 5 College Football Playoff since its inception. This could be the year that pollsters and the CFP committee see fit to omit Alabama from the 4-team Playoff and finally banish the Tide to only its 3rd meaningless January game since 2008.

Where LSU goes from here is simple: Atlanta. The SEC Championship Game beckons for the Tigers, and what Orgeron said both 2 years ago and in the lead-up to Saturday’s “Game Of The Year” ended up ringing true.

Yes, Ed, The Tigers are comin’. And yes, Ed, LSU does indeed have bigger games than this to play.

Alabama? No one knows from here.