But it was while they remained as guests of the Khan that one of the papal party, a nervous but intelligent young monk called Bohemond, discovered in his pack an ‘amulet’, as he called it. He had no idea how it had got there.

‘Philip eventually examined the amulet for himself,’ Thomas whispered. ‘He described it to me. It was a sealed box, the size of a man’s hand, slim and flat and smooth to the touch. It was pale, cream-coloured, but with coloured markings on its upper surface. It was made of neither wood nor ceramic nor metal - something none could identify. The Christians, huddled in their Mongol tent, exploring this thing, found they could not cut it with a knife, nor would fire burn it.’

But Bohemond himself discovered that if he pressed a certain marking on the upper lid, a green arrow, the box would speak to him - in good if stilted Latin, in a tiny insect’s voice. The legates were startled, terrified, intrigued. After much praying, and the application of much of their precious stock of holy water, they gathered around the box to hear what the imp in it had to say.

The imp spoke clearly of the future: of the next day, and of the years to come.

Of the next day, it described in detail Ogodai’s movements: the hour he would rise, the breakfast he would take, the councillors, ambassadors and generals he would meet, the letters he would dictate and have read to him, the wife he would lie with - and the cup of mare’s milk laced with Chinese rice wine that he liked to drink in the middle of the day.

On that cup of mare’s milk and wine, said the imp in its tiny voice, the future of the world depended. For it spoke then of what would happen if Ogodai lived - what would become of the world at the feet of the Mongols, in the future.

Mongol armies always advanced in the depths of winter, with their horses fat on the grasses of summer. So it would be, in just a few weeks, that they would fall at last on Vienna. The city would be plundered, torched and razed, and the Viennese scattered to starve on the plains. As the Mongols advanced further west, the Christian princes, hastily uniting, would raise another army, which would meet the Mongols in a pitched battle before Munich. The numbers were well matched. But the Christians would be lured by a false retreat into an ambush, a classic Mongol tactic. Munich would be smashed. The Mongols’ advance would be barely interrupted.

Next the Mongol force would split once more into three detachments. The first would strike at the Low Countries, plundering the rich young trading cities there before shattering them and slaughtering the population in the usual way. Holland’s dykes would be broken up; the sea would complete the Mongols’ victory.