by Dave Woods BBC Sport Online rugby league correspondent

The story goes that a certain Alex Murphy, mercurial half-back and Saints legend, sent a telegram to Wigan after his side's 21-2 win in the 1966 Challenge Cup final.

It read: Roses are red, violets are blues, St Helens 21 Wigan 2.

The two clubs didn't meet again in the Cup final until 1989, when Wigan gained revenge with a 27-0 thumping of the old enemy.

For sheer longevity of hatred, perpetual passions and a mutual longing for the other not just to fail but fall hopelessly flat on their faces, St Helens-Wigan takes the biscuit

Dave Woods

Hanley and Goulding played for both clubs

Somebody who beats you as often as you beat them to create a regular roller-coaster of smug triumph and utter despair.

Throughout most of their illustrious, trophy-winning histories, Wigan and Saints have been on a par.

Hence annual games become an obsession of the locals when league points are at stake.

Make the Challenge Cup the prize and you have a recipe for sleepless nights and churning stomachs days before the final.

There have been those who dared step foot in both camps.

Murphy himself, chief tormentor of Wigan in the 60s, became coach at Central Park and led them to a then rare Wembley final in 1984.

In the modern era, Bobbie Goulding, Sean Long, Andy Platt and Ellery Hanley are among those who changed allegiance.

Back in time, the great centre Eric Ashton coached and captained Wigan before returning to his home town St Helens to become club chairman.

Despite being born and brought up in the shadow of Knowsley Road, Ashton admits there were always those at St Helens who treated him with great mistrust because of his previous connections with Wigan.

Alex Murphy has played a key part in Wigan-St Helens battles

Every game these two play against each other seems to add to the legend.

You will never see a dull Wigan-St Helens match, they claim.

But when the two sides walk out at Murrayfield on Saturday, some of the rivalry may appear to have been diluted.

Too many out-of-towners in both sides for some peoples' liking.

Indeed, the St Helens team could have as many players born in the Wigan Borough as in the town of St Helens.

But something will catch them all - and all the intensity of the rivalry felt on the terraces will be felt by those on the pitch.

And St Helens and Wigan will provide another memorable occasion for the rugby league history books.

Pity they don't do telegrams anymore.