The Sydney Swans’ defence is in a phase of evolution and coach John Longmire sees young star Callum Mills as a key pillar.

Longmire firmly believes the 22-year-old has the weaponry to juggle roles in defence and on the ball but says he'll remain a backman in the foreseeable future.

“We’re looking at Callum down back and trying to come up with that back six that can play a lot of footy together,” Longmire told SEN.

“From Round 10 onwards last year, Callum actually won our best and fairest, so he’s a terrific player for us down back. We know he can play in the midfield, but we need to have someone who can replace him in defence and do the job he can do down back – and that’s not easy because he does it so well. So he’ll play a mix of midfield and back for us over the years but at the moment he’s a very, very good player for us down back.”

The 2019 retirement of stalwart defenders Jarrad McVeigh, Heath Grundy and Nick Smith stripped Sydney’s backline of 792 games’ worth of AFL experience.

It means names like Mills, Jake Lloyd and Aliir Aliir are now three of the most experienced members of the backline, which is ultimately led by co-captain and All Australian defender Dane Rampe.

Former defence coach Tadhg Kennelly praised Mills’ 2019 defensive work on not only some of the best small forwards in the league, but potent key forwards like Harry Himmelberg in Rampe’s absence.

There’s also often discussion around another former QBE Sydney Swans Academy prodigy in Isaac Heeney, who starred as a forward in 2019 but has also shown promising signs as a midfielder.

Longmire says while it’s crucial to have a firing midfield, top-end talent must be spread all over the ground.

“I don’t subscribe to the theory that you need all of your best players in the midfield,” Longmire said.

“You need to have a strong midfield. There is no question about that and we need to be able to strengthen that area, which we’re trying to do at the moment with a mix of speed and inside players. But you also need players at either end who can mark it and hit the scoreboard, in Isaac’s case, and players who can read the game and direct his teammates, in Callum’s case.”

Heeney underwent surgery on a broken thumb on January 30 and has since been restricted in training, but Swans Head of Football Charlie Gardiner expects the 23-year-old to be fit for Round 1.