East Bengal share the Salt Lake Stadium with rivals Mohun Bagan

Most people would assume an Indian sporting fixture that regularly attracts more than 100,000 people could only be one thing: a game of cricket.

But tell that to the people of Kolkata, who on Sunday gathered at the city's Salt Lake Stadium for the latest instalment of the 'Boro Derby', as East Bengal took on Mohun Bagan in what might well be the most well-attended, fiercely competitive and historically significant derby you've never heard of.

This was the 366th meeting of the sides - it has been played 134 more times than the Merseyside derby - and consumes the city, which is regarded as the game's spiritual home in a country of 1.3bn people.

Here, we take you inside a match steeped in tradition, watched by 'ultras' and regarded as a battleground for identity in India's third-biggest city.

A game with its place in history - and the record books

Mohun Bagan, founded in 1889, are one of the oldest football clubs in Asia. Their landmark victory while playing barefoot over the East Yorkshire Regiment in 1911 was the first time a local club had defeated a European one, ending years of British dominance in the early stages of the game in India.

This victory is considered a key event in India's fight for independence, so much so that the anniversary of the game on 29 July is recognised annually as 'Mohun Bagan Day'.

The rivalry was born in 1920, when East Bengal were founded by a frustrated chief executive of Mohun Bagan. Complaining that his team chose not to select a star player for a big game, he decided to start a rival club in the same city, taking the player with him and forming East Bengal.

Like so many classic city rivalries, the derby's lasting significance is rooted in the battle lines drawn off the pitch between the sides since their first meeting in 1925. The city's native population has tended to follow Mohun Bagan, with its immigrant communities from the eastern side (modern-day Bangladesh) opting for East Bengal.

This social and political rivalry is at the derby's heart, dividing the Bengali football population into either the green and maroon of Mohun Bagan or the yellow and red of East Bengal.

Ninety seven years later, the 'Boro derby' ('boro' meaning 'big' in Bengali) has created its fair share of history. Most notably, it holds the record for the highest attended sports fixture in India, with more than 130,000 people watching the 1997 derby, a 4-1 win for East Bengal.

Bhaichung Bhutia, still the only Indian to have played football in England, scored a hat-trick that day. He is the top scorer in the history of the derby with 19 goals, and has notoriously played for both teams during his career.

Bhaichung Bhutia, pictured in action for East Bengal in 2004, joined Bury in 1999

'Today there are no good words, only bad ones'

Mohun Bagan and East Bengal play in India's I-League, the older and more traditional of the nation's two top-flight football divisions. With both teams in the bottom half of the table, this particular meeting was all about local pride.

"I didn't sleep a minute last night - I never can the night before the derby," said one of the co-founders of the East Bengal Ultras group.

"All week we've been preparing and planning and on the day of the game, hour by hour, it gets more and more tense. If we don't win the derby, it's turmoil for us."

The Ultras unveiled their 'Tifo' - "we've been making this for the past three days and nights" - strapping the giant rolled-up banner to the roof of a car to be delivered to the stadium.

The Tifo reads: 'need I say more?' or 'do you understand sir?' and it depicts a Bengali comedian plus sugar, milk and tea. It refers to a classic jibe between the two sides.

"It's a kind of playful insult to the Mohun Bagan fans," he continued. "You'll see for yourselves later on the reaction it gets."

The derby presents the chance for the fans to compete as well as the players, with the historic identity and class differences taking centre stage.

"People are lovely here usually but on matchdays it's different," stated one of the fans, only half jokingly.

"Swearing and insults are part of the Bengali football culture sometimes. Today there are no good words, only bad ones."

Another fan spoke of how important this game is not just to the Kolkatans, but to the whole identity of the game across the country.

Kolkata is a city of 4.5m people, but its footballing reach spreads across India. There are fan groups for these clubs in states around the nation, and people travel thousands of miles for the derby, not to mention the millions that tune in to live television coverage.

"These two teams are the backbone of Indian football historically, and these games still get more headlines and media coverage than anything else," he said.

"More people care about this result than about the national team, or pretty much all of the other clubs put together."

Kolkata becomes a sea of colour on derby day

Fans fill the streets, bringing an unplanned halt to drivers' progress

Streets closed, insults thrown, riot police watch on

As kick-off drew nearer, the colours of the two teams became increasingly visible, flags held aloft by groups of supporters or fluttered from car windows.

It was a classic pre-match scene but everything was louder, brighter and busier. Street traders painted faces and sold replica shirts as fans shuffled towards the colossal Salt Lake Stadium, the cost of entering a modest 300 Rupees (equivalent to £3.33). Not bad for the biggest derby on the continent.

East Bengal's Ultras completed their signature 'Corteo' (procession), with hundreds of fans marching down the main road in a haze of smoke and drums. The streets became unofficially closed, traffic stopping and residents gathering to witness the colourful display.

Countless flatbed trucks and jeeps cruised towards the stadium, full to the brim with standing supporters, waving flags and chanting into loudhalers.

Vehicles full of rival fans found themselves toe to toe in the traffic, exchanging songs and insults as the noise levels grew.

Hordes of riot police watched on, but the mood was one of excitement and anticipation, despite occasional tensions.

'Who cares about the league? We've won the derby!'

Inside the gigantic oval stadium, East Bengal's 'Tifo' drew screeches from the disapproving Mohun Bagan contingent. Everywhere you looked, there were greens, reds and yellows stuck to every surface.

A tense beginning to the game was ended by Mohun Bagan's opening goal, a well-worked cross leaving an easy tap in for the Mariners. Their half of the ground erupted as the Bengal side fell silent, but they sought revenge swiftly, equalising from a flowing move four minutes later.

The momentum was with the Bengals as the game progressed, and their 44th-minute strike (a sublime scissor-kick finish) saw the red-and-yellow half of the stadium happier as the whistle blew, with the score 2-1 to East Bengal.

Half time was a whirlwind, a trip to the concourse offering a range of pop-up food and drink options, ranging from a blend of Indian snacks to American-style sports refreshments, not to mention replica jerseys for 500 Rupees (just over £5).

There was plenty of food but not a beer in sight as fans buzzed around beneath the stands during the break

The second half was equally frenetic, a combination of beautiful passing moves and scrappy route-one football. A skilful nutmeg from an East Bengal striker led to a scything tackle from Bagan's captain, already on a yellow card, leaving the Mariners down to 10 men and sending the crowd into a frenzy. When East Bengal scored from the resulting free-kick, the yellow-and-red half of the stadium erupted yet again.

Despite a spirited Mohun Bagan fightback - and a second goal that ensured a nervy final 15 minutes - East Bengal held on for a 3-2 win. It was their first triumph in seven derby matches (spanning 33 months, a fan reliably informed me), and the celebrations that followed lasted long into the Kolkata night.

As the vast Salt Lake Stadium emptied, there were groups clad in red and yellow dancing, singing and embracing one another. Despite the occasional moment of tension (the presence of the police or Mohun Bagan fans often flaring tempers), it was a joyous end to a dramatic and emotional derby day.

"This is what it's all about," concluded one of the Ultras group. "For years this game has been the battleground for identity in this city, through times of occupation, independence, war and immigration. It gives us a chance to validate our place here.

"Football is the way we bond, and the way we fight. Who cares about the league or where we finish, because we've won the derby again."

East Bengal's win took them up to fifth in the I-League, six points adrift of leaders Chennai City