But now a new study suggests its meaning may be a little more... salacious, news.com.au reports.
Experts already agreed that the monuments were aligned on the solstices but archaeologist Professor Terence Meaden believes that the builders of Stonehenge, and other megalithic circles such as Avebury, had in fact created a "play without words" in which one special stone cast a growing phallic shadow which penetrated the egg-shaped monument.
The professor examined nearly 20 stone circles across the UK and filmed their changing silhouettes at sunrise on ritually important days.
"My basic discovery is that many stone circles were built at a time of a fertility religion, and that stones were positioned such that at sunrise on auspicious dates of the year phallic shadows would be cast from a male-symbolic stone to a waiting female-symbolic stone," he told the Telegraph.
On certain days of clear sunrise, the study concluded, the shadow of the phallic Heel Stone penetrates the great monument during the summer solstice before arriving at the Altar Stone, which is symbolically female.