When AC Milan and city rivals Inter jointly revealed the design of their planned new stadium on Thursday, one thing stood out in particular - the name.

The 71,500-seater arena the clubs aim to share from 2031 onwards, replacing the iconic San Siro, will be called the Generali Stadium.

Generali is an Italian insurance company, and the firm has agreed to pay about 650m euros (£542m) for naming rights through to 2052.

The length and value of the agreement makes it one of the most lucrative naming-rights deals in sports history.

Stadium naming rights are, of course, nothing new in elite football. The champions of England and Germany both play in arenas built in the 21st century that have always been known by their sponsors' name, and plenty more stadiums across the continent have been partly financed by revenue from naming rights.

But in recent years, some clubs have struggled to sell them.

It was thought that both Tottenham Hotspur and West Ham would look to sell the rights to their new stadiums' names, but as yet neither have. Liverpool aimed to sell the name of a new stand they built in 2016 but no such deal has been agreed.

So, what do these stadium plans mean for AC Milan and Inter, what underpins the viability of expensive new football grounds, and what impact do culture and history have?

AC Milan v Inter Milan

AC Milan and Inter are owned by separate US-based investment firms and in the joint announcement described the Generali Stadium as "a new home for generations of supporters, and a destination designed to contribute to the cultural, economic and urban development of the city".

The demolition of San Siro has been discussed for decades, and the clubs believe its deterioration and lack of modern features are significant reasons behind their progressive fall lower down the pecking order at the top of European football.

The new stadium is expected to cost about 1.2bn euros (£1bn) to construct, and the clubs aim to generate income by selling just under 12,000 of the seats as premium or hospitality, and host a wider array of events like concerts and fixtures in other sports.

"This is the biggest stadium naming-rights deal in the history of global sports," AC Milan owner Gerry Cardinale told BBC Sport.

"That’s a significant achievement in its own right and especially in the context of having been done in Italy and what it means to bring Italy back to the world stage of football.

"But if you’re looking at this purely as an annual sponsorship payment, you’re missing the bigger picture.

"The stadium is what fundamentally transforms our economic model - matchday revenues, hospitality, premium experiences, entertainment and commercial opportunities.

"These are the things that allow us to compete with the biggest clubs in Europe."

AC Milan have played at San Siro for 100 years, while Inter moved in 1947. The two clubs paid 197m euros (£164m) to buy the stadium and surrounding land in 2025.

The plans for the new stadium have faced opposition from some supporters, with some Inter fans protesting outside the venue where the plans were announced by carrying a banner reading 'You will never extinguish the lights at San Siro' and chanting "Hands off San Siro".

"You cannot compete consistently with the best clubs in the world without having the infrastructure and economic model to support that ambition," added Cardinale.

"The Premier League has set the benchmark in terms of commercial development and infrastructure. Italian football has fallen behind, and we need to change that.

"This stadium is a massive step forward, not just for AC Milan but potentially for the whole of Serie A."

The two decades of naming rights paid for by Generali break down to about £27m per season - £13.5m per year, per club.

New stadiums are rarely built in Italy, with many Serie A stadiums in varying states of disrepair and in need of renovation before the country jointly hosts Euro 2032 with Turkey.

That means AC Milan and Inter have focused on selling a rare proposition.

"The 20-year deal is key - having that guaranteed long-term incomes gives the clubs security," said Dan Plumley - sport finance expert at Loughborough University.

"The money stacks up pretty well. Spotify pay around 20m euros (£17m) to sponsor Barcelona's Camp Nou per season, so now the Milan clubs aren't too far off that figure.

"What a lot of these partners are looking for is a long-term relationship because they can build their profile as expand around the world, pushing themselves into regions like Asia and Africa, and football can be very valuable for that.

"It couldn't be done at San Siro because everybody would have just carried on calling it that. Getting in early makes the sponsor part of the new history and is a really smart play from a business point of view."

Historically, the home of stadium naming rights has been the US, where the majority of arenas in most sports are known by a sponsor name.

In European football, similar deals have been most common in Germany, where major companies have direct ownership links to some of the country's biggest clubs including Bayer Leverkusen and Wolfsburg.

"It's really difficult to do naming-rights deals in English football because of our history and culture," said Plumley.

"The clubs and potential naming partners know that fans around the world could strongly oppose a deal, because it's less common here, so the value becomes less attractive."

Timing and performance on the pitch are key considerations when clubs are planning to sell the stadium name.

"As a club you don't want to just do a cheap deal and give the name away for a few million just because it's extra revenue," said Plumley.

"Clubs like Spurs or West Ham know there is a trade-off between not just agreeing something because it's a bit of extra value, having a deal that genuinely makes a difference financially, and doing something that the fans will tolerate.

"Sometimes the balance just isn't right, and some of the most successful clubs in the world would rather hold on and protect their overall value and hold off and sell when their performance is at its peak - being in the Champions League is key to that.

"Everton weren't in a position in terms of results to go out and get a big global name paying a huge amount every year, so a more local partner [the Hill Dickinson law firm] made sense."