Druids' ceremony greets the equinox

Ancient rites: Druids congregating on Tower Hill in east London yesterday for their annual spring equinox seed-sowing ceremony.

Also in London on the equinox, when the sun crosses the equator into the northern hemisphere, was the conference "Science and Stonehenge", organised by the Royal Society, English Heritage and the British Academy, which examined the mysteries of the stones on Salisbury Plain, Wiltshire, and was told of research which shows that they are almost 500 years older than previously believed.

It was thought that the stone circles were built between 2100BC and 1100BC. But using a new method involving mathematical analysis and more precise radiocarbon dating, English Heritage found that the main part, a ditch surrounded by an earth bank, was in active use from around 3000BC and the stones were put in place between 2550-1600BC.

The conference was also told that astronomical explanations of Stonehenge may be more scientific than archaeologists claim. Dr Clive Ruggles, who has studied astronomy and archaeology, said early arrangements of the stones reflected an interest in lunar symbolism while later ones were more concerned with solar symbolism. He said this could help understanding of the shifting belief systems of the site's creators.

Photograph: Dillon Bryden