Why was Stonehenge built?

Stonehenge is perhaps the most famous of all the henges, vast circular monuments constructed from wood or stone that litter the British countryside. The prehistoric monument was most likely erected in what is now England sometime between 3000 B.C. and 2000 B.C. and some of the stones were transported all the way from neighboring Wales — no small feat for a Stone Age civilization. 

It must have surely been a gargantuan effort and it begs the question: Why on Earth did they bother? Why did Stone Age people build so many henges? 

"The short answer is that I don't know and neither does anyone else," said Rosemary Hill, a historian and author of "Stonehenge" (Profile Books and Harvard University Press, 2008).

Related: What are rock cairns?

Before we go any further, it's important to note that,  technically speaking, Stonehenge isn't even a henge. The word "henge" is in fact a relatively recent term, first defined by British archaeologist Thomas Kendrick in 1932 to mean a circular bank with a ditch inside it and one or more entrances protruding through the bank. "But Stonehenge is the other way around, it's a bank inside a ditch," Hill told Live Science.

Another fun fact: Even ignoring the reverse order of ditch and bank, most henges still wouldn't have looked like Stonehenge because they were usually made from wood, which makes sense. Wood is everywhere, and is much easier to carve and transport, even if it isn't as durable. It wasn't until the 20th century that archaeologists realized that Britain once boasted a bounty of wood henges that have long since rotted away and vanished from sight. 

"After the First World War, when people started flying over the country, they started to see where these constructions had been because they left traces on the ground with their mounds. People hadn't really noticed until they got a bird's-eye view," Hill said. "They're also pretty much unique to Britain."