London — The world of professional sumo wrestling stepped outside of Japan for only the second time in its centuries-long history on Wednesday night, as fighters clashed on a specially constructed ring in the middle of London’s Royal Albert Hall.

The iconic venue in the British capital is hosting the Grand Sumo Tournament —the roughly 1,500-year-old sport’s most important competition — for the second time, drawing more than 44 professional wrestlers, or Rikishi, to compete in 100 bouts over five days. The only other time the tournament was held outside Japan was in 1991, when it also came to the Royal Albert Hall.

There are unique challenges in bringing sumo to London, as the contemporary national sport of Japan is rooted in two millennia of tradition, interwoven with the Shinto religion, and thus treated with the utmost respect and protection to ensure adherence to its rituals and norms. 

“One of the things that we’ve worked really hard at is to make sure that we have a good understanding of the cultural and religious significance that sumo has,” Matthew Todd, the Royal Albert Hall’s programming director, told CBS News. 

He said attention to detail was “really critical to the authentic presentation that we’re able to make here.”

That meant shipping 11 tons of clay from Japan to construct the ring, or dohyo, in the center of the concert venue, where the wrestlers compete. Shipping containers were at sea for three months making the voyage. A big team of ring attendants (yobisdashi), also had to make the trip from Japan — alongside 11 interpreters to help them communicate with British workers.

The roof for the dohyo, now suspended from the Albert Hall ceiling, was built in Britain, but its design is taken straight from traditional Japanese Shinto shrines, which, according to Todd, “helps to show that this is a sacred area,” in which routines and holy ceremonies are conducted as part of the tournament. 

It’s a vital step, he said, to ensure the Shinto gods are paid their due respects before the fights.

Sumo is deeply intertwined with Japanese culture and religion in ways that many Western sports fans may find difficult to comprehend. According to legend, it originated as a ritual to ask the gods for a bountiful harvest, but it transformed over almost 2,000 years into the sport it is today, drawing competitors still primarily from Japan, but also from around the world.

Many of the most recent champions have been from Mongolia, and this year’s tournament features two rishiki from Ukraine. While Americans have competed successfully in past tournaments, there are no U.S. rishiki competing in this year’s event in London.

The nuance of the wrestling competition itself can also be difficult to fully grasp, with 82 winning techniques called kimirate, numerous ranks and divisions and a host of other rules. So to help translate all this for a largely Western audience, in-ear English language commentary is provided at the Royal Albert Hall, alongside video replay screens to describe and explain the bouts, which can sometimes end in just seconds when a competitor is forced out of the ring.

The wrestlers themselves live an incredibly regimented life. They are forbidden from driving cars and, somewhat counterintuitively, eating breakfast, and are normally required to take a long nap after their hefty lunch, to help them pack on the pounds. 

The average weight of a rikishi is about 330 pounds, but some tip the scales at 550.

They have been given some leave during their visit to the British capital to enjoy themselves, however — with organizers likely seeing the value in some degree of publicity. 

During the lead-up to the tournament, social media platforms were full of photos and videos of the traditionally kimono-clad wrestlers sightseeing around London.

The Albert Hall will also be graced this week by the presence of two yokozuna, the highest ranking of all sumo wrestlers. The word yokozuna is generally translated as grand champion, but it translates literally to “horizontal rope,” in a reference to the special rope worn around their waists to display their rank.

Once a rishiki is promoted to the rank of yokozuna, they keep it until retirement. In nearly 400 years of professional sumo, only 75 men have attained the vaunted grand champion status. The honor typically requires not only multiple consecutive championship wins, but approval by a dedicated council that judges rishiki on their wrestling skills, but also a range of other personal attributes.

The tournament is due to end on Sunday, when the wrestler with the most victories in the ring will be crowned this year’s champion.

The field is considered wide open this year, but many, especially back at home in Japan, will be hoping for 25-year-old Yokozuna Onasato, the country’s first grand champion in almost a decade, to emerge victorious.