The existence of Stockholm as Sweden’s dominant capital is due overwhelmingly to post-glacial rebound. Without it, the old Viking sea route through Södertälje may have stayed open, and Stockholm would probably have remained a small fishing settlement. 1/n

In Brussels, the Taxis postmistress Alexandrine ran a post office that may have housed the first "Black Chamber" in Europe, during the Thirty Years' War.

Because it covers the whole body, the armour weighs 42.6 kilograms. That is twice the weight of a standard battle armour of the time.

In the spring of 1241 Europe stood on the edge of the abyss. In two days the Mongols landed two crushing blows: in the north they broke a combined Polish and German force at Legnica, and in the south the main army under Batu and Subutai destroyed the Hungarian army at Mohi. The road to Vienna lay open. Yet in the spring of 1242 the unbeatable army suddenly broke camp and went back east. For a long time this retreat had one textbook explanation: the death of the Great Khan Ögedei. On that reading Batu turned back to take part in choosing the next ruler (though in fact he settled on the Volga and never showed up at the kurultai). Modern climate research points somewhere else. Europe was saved by mud, and high politics had little to do with it. After several dry years, early 1242 turned cold and wet. The Great Hungarian Plain, a perfect base for cavalry, became one vast swamp once the spring floods came. For the Mongol army this was a supply disaster: - Flooded pastures left hundreds of thousands of horses without feed (every warrior had three to five spare mounts). - Soft ground ruled out fast manoeuvre, the nomads' main tactic. - Siege engines, needed against Europe's stone castles, could not be hauled through the bogs. It looks as though Europe was saved by the weather, and the khan's death came second. The weather took from the best army in the world its strongest card: speed.

In 67 AD Nero himself struck the ground with a golden pickaxe to open work on the Corinth Canal. Six thousand Jewish prisoners cut into the rock. A year later the emperor was dead and the project was abandoned. The canal was only finished in 1893, along exactly the ancient line. A relief of Hercules carved by Nero's workers 2,000 years ago still survives in the sheer wall.

The world's main financial street, Wall Street, is literally named after a fence. In 1653 the Dutch walled off New Amsterdam on the north side, bracing for a land invasion. The plan was solid until 1664, when the English simply sailed in from the sea, straight into the harbour. The governor was itching for a fight, the townspeople thought he had lost his mind and handed the town over. In 1699 the wall was torn down, but the name of the most useless defence ever stayed.

In 1993 archaeologists found Bronze Age skeletons in a cave in the Harz Mountains in Germany. The bones were about 3,000 years old. A lab took DNA from them and compared it with samples from people living nearby. Two men from the same village, Manfred Huchthausen and Uwe Lange, turned out to be descendants of the people in the cave. That is about 120 generations in one place.

Leif Erikson Day today. The only secure date we have for the Norse in America is 1021. It comes from tree rings at L'Anse aux Meadows in Newfoundland. The wood was cut that year, 471 years before Columbus sailed.