On Sunday, you saw the fall of the Roman Empire.

Different, but the same. Like the 476 Romans, the 2017 Broncos collapsed before our very eyes. The once-mighty Broncos are mighty no longer, and it’s something you’d better get used to. An incredibly fun ride that began Oct. 23, 2011, when second-year quarterback Tim Tebow was hesitantly handed a starting role, then continued to roll on with four fantastic seasons behind the great Peyton Manning, has reached its pathetic end – with a trio of quarterbacks who probably shouldn’t be on next year’s roster.

It’s over, Denver.

Alexander Demandt, a German historian (“Al Da Man” to his friends), once penned 210 reasons as to why the Roman Empire finally fell. Reading this account would surely be a long and boring endeavor, but the Cliffs Notes version probably pins blame about like this: The Romans made a series of mistakes and miscalculations, which eventually became too much to overcome.

Just like the missteps in Rome, each individual mistake made by John Elway, his scouts, his coaches and his players was not insurmountable. Combined though, the sum of all blunders finally was too much to bear. The collapse was so painfully obvious, television stations outside of Denver flipped from the Broncos game to, well, pretty much any other game being played. It was so bad, plenty of folks in Denver threw in the towel as well, missing the ugly final result: 14 penalties for 105 yards (!), a final score of Denver 23, Philadelphia 51 and a 3-5 record that feels more like 0-8.

When exactly Rome began to fall has been up for debate – Demandt and his dissenters argued like Skip and Shannon – for thousands of years. When and why the Broncos started to slip, will be hotly debated from now until the end of this NFL season. If you’re interested in formulating a timeline, here’s some food for thought:

You shouldn’t ungratefully ask a future Hall of Fame quarterback, who’s coming off three consecutive AFC West titles, a trip to the Super Bowl and three of the greatest passing seasons in the history of the NFL, to restructure his five-year contract.

And when that Hall of Famer finally hangs it up, after bringing home the Vince Lombardi Trophy with the help of a world class defense, you can’t mishandle his replacement, who (at the time) appeared to be more than adequate.

When you do mishandle the successor at quarterback, you’ve got to come up with a solution — one that considers that narrow window inside which Super Bowls can be won.

You certainly can’t move up in the draft in hopes of finding Peyton Manning’s successor… and miss.

And just in case you miss, you need a backup plan, something more along the lines of Colin Kaepernick — not Mark Sanchez, and especially not Trevor Siemian.

You can’t watch Siemian be average for an entire season, while the future of the position rides the pine. In that scenario, there’s no way to know if you’ve missed or not. There’s no way he gets any better, either.

You can’t bank on Tony Romo and then let him become a broadcaster.

You can’t have too much pride to sign a quarterback you tried to sign the year before. (Where would the Broncos be right now with Kaepernick?)

You can’t waste an entire camp — splitting reps and carrying on a charade in the name of “competition” — not naming your starting quarterback.

When your starter finally appears to be the average player everyone thought he was, you can’t blame the offensive line.

Well, you can actually.

That’s a reminder. You can’t waste second- and third-round draft picks on guys like Ty Sambrailo and Michael Schofield. You can’t miss on free-agent signings like Menelik Watson, Donald Stephenson or Russell Okung.

And you certainly can’t hand the entire mess to a first-year head coach who appears to be in over his head.

Come to think of it, how did that guy get Denver’s most scrutinized job anyway? Why let go of your defensive coordinator — the strength of your Super Bowl winning coaching staff — and bring in a never-been-a-head-coach, defensive coordinator to be your head coach? Just months before you hired him, in fact, he “led” his Miami defense to a No. 29 ranking.

You can’t do that.

If the defense is the strength of your team, and your offense is struggling, why not hire the brightest offensive mind in the game, who, by the way, has a previous tie to the organization?

You can’t do that?

The head coach can’t keep trotting out a quarterback who can’t play. After halves of complete incompetence. After getting shut out. After it’s obvious the offense is going nowhere. Not only is his football team losing, but he still doesn’t know what he’s got in the fellow who is supposed to be the quarterback for years to come in Denver.

You can’t ask the defense to do everything. You can’t cut a Pro Bowl safety, a leader of the defense, a week before the season. You can’t let rumors rumble that you might trade your future Hall of Fame cornerback the week before you ask him to try to shut down one the best offenses in the NFL. No matter how great that defense is, sometimes enough is enough.

You can’t do all of that. When you do, you get 51-23.

Rome wasn’t built in a day, and neither were the Broncos. Both — Rome and the Broncos — were once great, and they were both built by great men. There’s no denying that.

But Rome didn’t fall in a single day, either. It took years of miscalculation and the arrogance that comes with being on top for a long, long time.

Sound familiar?

This dynasty (the Broncos are as deserving of that label as any current franchise in the NFL) has collapsed. Sunday, the crumble looked complete.

The Broncos will be back – you can count on that – but it could be awhile.

Remember, Rome wasn’t built in a day.