Vikingeborgen Fyrkat in Mariagerfjord

You're standing at Fyrkat, a Viking Age ring fortress just outside Hobro in northern Jutland. Have a look around. That grassy rampart forms an almost perfect circle. Inside, it measures a hundred and twenty metres across, and at its base the wall is twelve to thirteen metres thick. See the four gaps? Those were the gates, set exactly opposite each other. Two wooden roads ran between them and crossed at a precise right angle in the very centre.