The Course

Choose between the Imperial 100-Mile Centurion Triathlon, the Metric 100-Kilometre Centurion Triathlon and the Legionnaire Sprint.

The Centurion Triathlon is based in the stunning amphitheatre of Stanborough Lakes, Welwyn Garden City. It is one of Hertfordshire’s most scenic open water swimming venues.


Cut off – 1 hour 15mins from start

The swim distance is 2 km (1.25 miles) both for the Imperial (100 mile) and Metric (100Km) distances. That means completing two rectangular laps clockwise. Athletes exiting the water without mishap will run the 100 metres across grass to transition.

However, the fate of those missing the one-hour cut off is uncertain!

(The Legionnaire Sprint will use a slightly shorter 750m loop, and will have no cut off)


Cut off – 7 Hours after start

BLACK (Outward)

From Stanborough lakes, you will set off down some fantasticly fast roads, including Coopers Green Lane and the B651 towards Wheathampstead.

MAROON (Main Loop)

The main loop begins by heading along Kimpton road and turning left up Heath Hill. You will then be greeted with an 8km straightaway where you can pick up some serious speed! After negotiating Little Almshoe Road, St Albans Way and School Ln, you will arrive at the feed station. We have bananas, energy gels, energy drinks, sweets, crisps and water bottles to keep you going. Continue along Back Ln, Parsonage Ln and Church Rd, then turn left on Lilley Bottom Rd. From here, it’s another long straightaway into Whitwell. Climb up Horn Hill, all the way back to Kimpton, to complete the lap.

The Imperials will complete 4 laps, wheras the Metric combatants will complete just 2.

RED (Back)

Double back along Ballslough Hill, then turn left onto Lamer Way. Those of you who have completed the Hertfordshire Triathlon will be familiar with the final section of the route. Follow the B653 all the way to Brocket Rd and Stanborough, before the final turnaround to the dismount line.

The Legionnaire Sprint will use the southernmost triangle of the course to make an undulating 20.3km lap
( There is no time cut off for the Legionnaire bike.

Run Course

Cut off – 10.5 Hours after race start

After racking your bike it will be time to run. You will complete a partial lap of the Stanborough park where your friends and family will be able to cheer you on.

You will then leave Stanborough and head underneath a railway bridge, where you will be greeted by the first of two feed stations out on the course.

The second feed station is very close to the QE2 Hospital, once again, with water, energy drinks, bananas, energy gels, sweets and crisps all to choose from.

Head back towards Stanborough and pass the feed station again, but this time, you will turn left into Stanborough park and complete the final part of your lap.

Metric contestants will complete 2 full 8.05km laps, wheras Imperials will complete 3, for them totalling 15 miles.

Only then will you be A CENTURION!

 The Legionnaire Sprint will stay within the park and complete 2 x 2.5km laps. 

Quick Event Info

Centurion Tri
Imperial 100 Mile: 1.25-Mile Swim, 84-Mile Bike, 15-Mile Run
Metric 100K: 2Km Swim, 82Km Bike, 16Km Run
Legionnaire Sprint 750m Swim, 20.3Km Bike, 5Km Run
NB: Please check venue pages for exact distance options available at each
Organiser: ActiveTrainingWorld
Race Info: