About a thousand years ago, a European leader fearful of losing his power set off in a foul temper to make peace with the Pope. Having crossed the Jura, he put on a hair shirt and removed his shoes. Barefoot and in the depths of winter, he crossed the Alps, reaching the Tuscan citadel where his Holiness was installed in January, 1077. The gates were shut. They remained so for three days, during which the penitent northerner added to his own discomfort by fasting. At last he was let in. Falling to his knees before the Pope, he begged forgiveness for his arrogance and was readmitted to the Church, only to be excommunicated again soon after he got home.

Reconciling the swollen vanities of European potentates was ever arduous. The Prime Minister should be thankful that the ordeal he faces tomorrow in Lisbon is logistically trivial compared with that endured by Henry IV on the road to Canossa. He will rise and breakfast at Number 10, face questions from the Commons Liaison Committee, then board a chartered jet and be in Portugal for lunch. He will, regretfully, miss the official signing ceremony for the European “treaty” that dare not speak its name, but will sign it in private, unphotographed. He will wear shoes.

He should also be safe; summit security is a lesson learnt from history. In 460 AD, when English unity was fragile and Europe barely a concept, the ill-starred King Vortigern summoned the leaders of the island's insurgent Saxons to a multi-purpose banquet to mark the signing of a peace treaty and his marriage to a Saxon belle. But soon after the hors d'oeuvres, and in violation of their proto-ASBOs, his guests unsheathed long hidden knives and slaughtered every Briton present except Vortigern himself.

Whatever else about Lisbon fills Mr Brown with dread, it is not a bloodbath. Nor can he reasonably fear an untimely leak or scoop. The last time the text of a major treaty hit the streets before its signatories intended, those streets were London's and the text was — naturally — in The Times. Henri de Blowitz, our legendary Paris correspondent, had spent decades cultivating the Great Powers' crown princes and proconsuls to the extent that they pummelled him for information even more shamelessly than he did them. In 1878, handed the final wording of the Treaty of Berlin before Bismark himself, he left town with it sewn into his coat lining and telegraphed it to Printing House Square from Brussels. Every emasculatory detail of the Treaty of Lisbon, by contrast, has been known for months to all those with the energy to read it.

Mr Brown does face two real risks. The first is the certainty that this treaty will be vilified by history — and not just by history — like the Treaty of Worms, by which Britain sought to drive a wedge between Sardinia and France in 1743 with the help of massive secret bribes to Austria. That sordid deal was condemned immediately in the Commons by Pitt the Elder as “one of the most destructive, unjust and absurd that was ever concluded”. The second risk is of ridicule, in verse. “Sign, sign, sign, they said / “ (of Magna Carta). “Sign King John, or resign instead! / (And King John signed.)” In which context there is one thing to be said for “Gordon”. It wouldn't scan.