Tennessee's defense reminds us of a titan of antiquity, a pigskin Colossus of Rhodes that lords over the entrance to the end zone like no team in modern history.

The 6-0 Titans are the only undefeated team left in football, and they've done it old-school style, pounding the ball on the ground and playing lights-out defense (league-leading 11.0 PPG allowed).

In fact, six games into the season, Tennessee has surrendered just one TD pass (that's 1, for those of you keeping score at home), which puts the Titans on a pace to surrender just three TD passes all year. They've added 10 INTs to the total, for a 1-to-10 TD-to-INT ratio that's virtually unprecedented in NFL history.

If the season unfolds this way -- and the Titans go an entire year surrendering just three TD passes, or something close -- it would go down as one of the greatest defensive performances in all of NFL history.

We live in an era that favors the passer and the passing game. We live in an era of inflated passer ratings and passing numbers. We live in the era of the two most productive TD-tossing seasons in NFL history (49 by Peyton Manning in 2004; 50 by Tom Brady in 2007).

Put most simply, teams in the 21st-century NFL pass the ball more often for more yards and more scores than they ever have before.

But even with the statistical and historical decks stacked against it, no team in modern football history has come close to being as stingy against passing offenses as Tennessee is right now.

The Super Bowl Era record for fewest TD passes allowed is held by the champion 1973 Dolphins, a defensive juggernaut (10.7 PPG) that surrendered just five TD passes in a 14-game season.

Looking for a team that allowed fewer TD passes than the 1973 'Fins?

You have to go all the way back to the wartime Giants of 1944 -- they gave up three TD tosses on their way to an 8-1-1 record, before losing to the Packers in the NFL championship game.

But it's not even fair to compare those teams to the 2008 Titans.

Both the 1944 Giants and 1973 Dolphins played in eras that favored defenses and discouraged passing offenses. The NFL was depleted by the war when the Giants set their defensive standard in 1944. Plus, the passing game in general was in its infancy in the 1940s.

The 1973 Dolphins, meanwhile, played at the height of what the Cold, Hard Football Facts call the NFL's Dead Ball Era -- a period in the 1960s through 1977 when it became increasingly difficult to score and, in particular, to pass the ball.

By 1977, there was such a dearth of offense that the NFL was forced to institute wholesale rule changes to open up the game in 1978, spawning what we now know as the Live Ball Era.

The NFL also went to a 16-game schedule in 1978. So the rule changes and the longer schedule since then give us the best test group with which to compare the 2008 Titans. During this Live Ball Era, only the 1978 Broncos and 1990 Steelers, have surrendered fewer than 10 TD passes in a season (nine each).

In fact, here's how some of the NFL's most famous defenses have performed against the pass in the Super Bowl Era:

The 1966 Packers won the Super Bowl behind a pass defense that surrendered 7 TD passses and picked off 28 (14 games).

The 1970 Vikings dominated with a pass defense that surrendered six TD passes and picked off 28 (14 games).

The 1970s Steelers won four Super Bowls behind the famous Steel Curtain defense. In their best year, the championship 1975 season, they allowed nine TD passes and picked off 27 (14 games).

The 1985 Bears won the Super Bowl and boast one of the most famous defenses in history. They allowed 16 TD passes and picked off 34.

The 2000 Ravens won the Super Bowl and boast the stingiest defense of the Live Ball Era (10.3 PPG). They allowed 11 TD passes and picked off 23.

The 2002 Buccaneers won the Super Bowl behind one of the most stifling pass defenses in modern NFL history. They allowed 10 TD passes and picked off 31.

The 2008 Titans, meanwhile, are on pace to allow three TD passes and pick off 27.

So the Titans have some wiggle room as they attempt to set a modern standard of defensive stinginess.

They'll need it, too.

One reason for Tennessee's success so far is that they've faced a series of poor passing offenses, including Kansas City (31st in passing yards) Cincinnati (30th), Baltimore (25th) and Jacksonville (20th).

The future schedule includes two games against Peyton Manning and the Colts, not to mention showdowns with Brett Favre and Ben Roethlisberger.

The Titans right now stand as one of the elite pass defenses the game has ever seen. We'll be watching to see if this pigskin colossus is still standing there at the end of the season.

SI Apps
We've Got Apps Too
Get expert analysis, unrivaled access, and the award-winning storytelling only SI can provide - from Peter King, Tom Verducci, Lee Jenkins, Seth Davis, and more - delivered straight to you, along with up-to-the-minute news and live scores.