German rivals Jan Frodeno and Patrick Lange will lock horns on home turf when the Ironman European Championships takes place around Frankfurt tomorrow.
Both male and female elite fields will begin with a 3.8 kilometres swim in the waters of the Langener Waldsee on the German course, where temperature is set to be between 22°C and 24°C.
They will then complete a 180km bike course before a 42km marathon run finale.
The event will then finish in the historic heart of the host city.
Lange is the reigning Ironman world champion while Frodeno won the global event in 2015 and 2016.
He was also the Beijing 2008 Olympic gold medallist before moving up in distance.
Frodeno beat Lange in a half Ironman race in Kraichgau last month.
Josh Amberger of Australia, Michael Weiss of Austria and Andreas Raelert of Germany will be other contenders in an event when non-Europeans are also able to enter.
Switzerland's three-time reigning world champion Daniela Ryf will start as favourite in the women's event.
It will mark her first Ironman of the season.
Sarah Crowley of Australia, Anne Haug of Germany and Sarah True of the United States are among other leading entries.