When in 1519 the invading Spanish commander first set eyes on the Aztec city of Tenochtitlan he wrote ‘When we saw so many cities and villages built in the water and other great towns on dry land and that straight and level causeway going towards Mexico, we were amazed and said that it was like the enchantments they tell of in the legend of Amadis, on account of the great towers and temples rising from the water.’

This was on the site of what is now Mexico City, and at a time when Henry VIII had been king for ten years. He was invading France, not very effectively, but the Spanish were taking over the New World, using guns and biological warfare in the shape of simple diseases like measles and flu, which wiped out thousands of Native Americans.

When the Spanish arrived, the Aztec community had been flourishing there for about 175 years, and had become one of the largest and most powerful of the civilizations in all the Americas. Boys and girls were educated, and women had more rights than in most parts of the world. However, the Aztecs were a brutal people, and their Great Temple pyramid Templo Mayor, which was rebuilt several times, had a shrine for the god of storms and a shrine to the god of war. According to Unsolved History they made offerings to the war god in human blood, and needed such vast quantities of the stuff that they had to wage almost continuous wars in order to find enough victims.

Could they really have sacrificed 20,000 people in four days? How could they have found so many enemies? How could they have marched them all into the city? Where did they imprison them? How physically could they kill so many, and what did they do with the corpses?

I am always a bit suspicious when archaeologists see a groove in a big stone and say that it is obviously a channel for the blood from human sacrifices. Grooves can have other uses, and although human beings are bloodthirsty creatures, and have always enjoyed killing one another, there must be many other ways of trying to please the gods. Nevertheless in the case of the Aztecs human sacrifice really does seem to have been a regular event; so perhaps their grooves really were for blood.