Slowly,Arsene Wenger has assembled a strong and deep defence.

The signing of Gabriel Paulista is unlikely to change our first choice XI any time soon but it is, nonetheless, a huge step in the right direction.

At a time when the club has more money, it is significant we can spend £11.3M on a player who won’t always be first choice.

We have depth at the back and are now capable of building a squad – not a team, a squad – which can challenge for all of the major honours.

With our financial constraints lifted we have been bulking up the squad gradually over the past few windows, and now have suitable depth across the back four.

We now have at least two players (of adequate quality) for every position in the defence as Arsène Wenger continues to build the best squad he’s ever had.

What follows is not an excuse for not building it earlier, but we have been far from fortunate as I will show.

The one criticism that can be levelled at Arsenal is that we knew Laurent Koscielny had issues with his Achilles in the summer but didn’t act then and paid the price as he missed nearly two months.

Beyond that we have been more than a little unlucky.

Mathieu Debuchy has managed to start just 10 of the 23 Premier League games since his move from Newcastle. Two of those games came in an unfamiliar role (in which he played well) due to injuries elsewhere.

Both of his long-term injuries have been from bad luck (Manchester City) and pure thuggery (Stoke) and we will still be without him for some time.

Koscielny and Debuchy – half of our first choice back four – have together missed twenty-two Premier League matches through injury.

Arsenal v Chelsea

We started the season with six senior defenders; the same number as Chelsea.

They, however, have enjoyed the luxury of having John Terry and Branislav Ivanović play every game.

Cesar Azpilicueta has managed 18 (he was banned for two and dropped for the other three) and Gary Cahill has also gone the whole season so far without injury and been an ever-present in the Chelsea squad.

Ending up with Debuchy and Nacho Monreal at centre-back was preventable, but is still unlucky.

For years we have lacked depth at the back.

Look beyond the first-choice pairing of Sol Campbell and Kolo Touré and the Invicible squad had a retiring Martin Keown and Pascal Cygan as cover. At full-back the cover consisted of 17 year-old Gael Clichy and first choice centre-back Touré.

Since then Mikael Silvestre and Sebastian Squillaci have – after Cygan – completed a triumvirate of troublesome Tricolore options to wear 18 in the middle of our defence.

Other one-time understudies Phillipe Senderos and Johan Djourou have shown some periods of good form but tailed off and became known as two more accident prone defenders to pull on the red and white.

After an excellent first season, Thomas Vermaelen struggled with injuries and then form. He never really formed a good partnership with Koscielny and eventually left last summer (and has been injured ever since).

Stylistically the two didn’t fit.

Vermaelen could play better with Per Mertesacker but not with the Frenchman. Likewise Calum Chambers started this season playing well alongside Koscielny; when paired with Per Mertesacker we were, quite simply, at sixes and sevens at the back.

Nacho Monreal has also played well alongside Mertesacker but looked shakier (and at fault for one goal) when he partnered Koscielny against Brighton last weekend.

A back four is all about partnerships which compliment each other and last season we were blessed with the fitness of Mertesacker and Koscielny; they form a perfect pair.

Now, in theory, we have that in depth., more so than any other Arsenal squad has ever had.

At right-back Debuchy may not even be first choice any longer thanks to the emergence of Héctor Bellerín.

The Spaniard was a winger in the Barcelona academy and it shows – his pace and delivery are everything Wenger looks for in a wingback, while he is showing he is also a very adept defender.

He looks set to be Arsenal’s right-back for a very long time but right now has competition in the form of two summer signings who, between them, cost the best part of £28M.

Not bad, eh?

On the left-hand side we have two players who would both be first choice for almost any other team in the country.

Kieran Gibbs was solid for all of last season and is England’s best left-back, but right now Gibbs can’t budge Monreal, who is ever improving. Solid defensively and effective on the occasional foray forward, Monreal is becoming more and more important to us.

The combinations of Bellerín/Monreal and Debuchy/Gibbs give Arsène Wenger the perfect balance he likes from his fullbacks with one providing a cutting edge and the other being more conservative. The fact we have (at least) two options on both sides is massive now.

At centre-half we have that fantastic pairing of Mertesacker and Koscielny. The real problem area has always been here, when one of the first-choice defenders has been missing.

Perhaps that’s finally over.

When without Mertesacker we also now have Calum Chambers.

Aside from the game at Besiktas he was fantastic at the start of the season next to Koscielny. Good in the air and on the ball, his reading of the game is already good and will improve.

He’s happy to stand off and let his partner attack the ball. A great understudy for Mertesacker.

And Koscielny? That’s where Gabriel Paulista comes in.

By all accounts the Brazilian is tenacious and hunts the ball.

Blessed with pace and dominant in the air, he makes a huge number of interceptions.

Sounds a lot like Koscielny, doesn’t he?

At just 24 he will only improve and has plenty of time to adapt to England, though his style and approach suggests that he won’t have much issue with the fast or physical nature of the Premier League.

Defensive options

Finally The Arsenal have options all across the back four. A good mix of experience and youth, we have players at their peak and players with a huge amount of potential.

Our depth has been questioned and criticised for years but now, finally, the first choice back-four has complete and adequate cover.

Times have changed and, with more money, the playing field is being levelled.

This regular Sunday column will touch on our tactics from time to time but probably after more interesting games than the one against Aston Villa on Sunday afternoon. Watch this space next weekend after the North London Derby