Texas forward Mohamed Bamba, a versatile big man, should go early in this week’s NBA draft. (Sue Ogrocki/Associated Press)

For as long as basketball has existed, size has been considered almost a prerequisite to success. Consider how many of the dominant teams in NBA history had dominant big men — George Mikan, Bill Russell, Wilt Chamberlain, Kareem Abdul-Jabbar, Hakeem Olajuwon, Shaquille O’Neal and Tim Duncan — at their core.

The modern NBA, though, finds itself in a far different place than previous eras. The two-time defending champion Golden State Warriors had six centers on their roster last season — and none was as effective as the team’s 6-foot-6 power forward, Draymond Green. The Houston Rockets presented the Warriors with their biggest challenge during the playoffs, and the Rockets spent large portions of the Western Conference finals with another 6-6 player, P.J. Tucker, manning the middle.

As teams increasingly emphasize perimeter play and three-point shooting, the need for versatile wing players has never been greater. And as a result, there is an ever-expanding glut of big men who are finding it harder and harder to land consistent roles with any teams — let alone the league’s best.

“I think that what you’re seeing in the league now is really one through four in a lot of ways are two-way players,” Oklahoma City Thunder Coach Billy Donovan said. “There are the guys that can handle, pass and shoot, and dribble and make plays on offense. Then there are guys that defensively can go to multiple positions.

“That’s, I think, what you’re seeing. You’re seeing a lot of guys that have flexibility to do a lot of different things, from playing with the ball in their hands to playing off the ball to playing pick and roll to shooting threes. Then you’re seeing them be able to have length in size to be able to guard multiple positions.”

Those changes are what make the top of Thursday’s NBA draft so interesting. Five of the top six picks could be big men, with Deandre Ayton, Marvin Bagley, Mohamed Bamba, Jaren Jackson and Wendell Carter all projected to be among the first eight players off the board.

That might seem odd, given the league’s direction. But even with this nearly unprecedented emphasis on going small, an elite big man can still move the needle — especially a big man capable of fitting into today’s smaller, faster league.

Specifically, that means big men who can move their feet quickly enough to switch on the perimeter and/or be a capable rim protector defensively, and who are also able to shoot from the perimeter effectively. Players who can do two of those things remain useful. The rare ones who can do all three? They remain special, which is why players such as Joel Embiid, Karl-Anthony Towns, Kristaps Porzingis, Rudy Gobert and Clint Capela remain hugely valuable.

Teams picking at the top of this year’s draft clearly are hoping the big-man prospects are capable of sliding into that stratosphere.

“Just talking to teams, I would say there is a confidence level these guys can all play against [power forwards] and [centers],” ESPN analyst and former NBA front-office executive Bobby Marks said. “They’re not all back-to-the-basket players. They can switch, which you know is important, and they all can shoot.

“I don’t know if they’re the Patrick Ewing type that is the traditional center. … They all are almost the modern-day [center]. Those are the guys who can stay on the court at the end of the game.”

That so few true centers are capable of staying on the court at the end of NBA games, though, shows just how much the sport has changed. More often, teams are instead inserting a 6-6 or 6-7 player at center to allow for more defensive versatility and to play at a faster pace in the decisive moments.

The Brooklyn Nets, for example, spent large chunks of the season experimenting with Rondae Hollis-Jefferson — a 6-7 forward who weighs 215 pounds — at center, a move Coach Kenny Atkinson favored because it gave him more options.

“I like it,” Atkinson said. “What people forget is that he’s 6-foot-7, but has a 7-foot-3 wingspan. I feel like we don’t get hurt when he’s at the five.

“I think because of where we are, we have to keep trying unconventional things, and we’re going to keep doing it. It’s a little unconventional, but I do think it can be successful in this league, no question about it.”

For proof, all Atkinson had to do was watch the Western Conference finals. Houston and Golden State spent large stretches of that seven-game series with the floor filled almost exclusively with wing players, with few true bigs — Capela for Houston, and Kevon Looney and Jordan Bell for Golden State — receiving consistent minutes.

The rest of the time, both teams were fielding lineups full of three-point shooters and players capable of switching onto anyone on the court. It was the pinnacle of the sport’s recent evolution.

“When you find guys who can make threes and defend,” said Warriors Coach Steve Kerr, “I mean, that seems to be the name of the game.”

That’s why the irony of this draft class arrives later in the first round. As the playoff teams finally begin to pick, they’ll be staring at a glut of wing players. Several wings who could be picked in the back half of the first round — from Grayson Allen to Jacob Evans to Melvin Frazier to Donte DiVincenzo to Khyri Thomas — could immediately step in and contribute for playoff teams, filling exactly the role Kerr described.

Be it in the draft, free agency or beyond, those are the players NBA teams now covet. The best teams — Houston, Golden State, the Cleveland Cavaliers and the Boston Celtics — have a plethora of them. The teams chasing them? They can’t get enough.

“I think it’s just very hard to find wings that have that ability to dribble, shoot, and defend,” one scout said. “That’s what makes them so special.”

And that’s why teams will keep looking for them.

Read more NBA coverage from The Post:

NBA mock draft 2018: Deandre Ayton to go No. 1 … but then what?

Trades within the lottery could jolt an already intriguing NBA draft this week

Ahead of the NBA draft, here’s what the experts project the Wizards will do with the 15th pick

Robert Williams looks to bring defensive ability to Wizards, give them the athletic big they need