Stonehenge greeted the summer solstice this year with over 8,000 visitors, showing why many believe it to be an ancient timekeeper.

Wednesday, June 21st is the longest day of this year in the Northern Hemisphere, the day the sun circles directly above the Tropic of Cancer. For many, it’s a day of significance. Druids, pagans, and members of many other religions mark it as important, along with plenty of people of no particular faith.

No one knows specifically why Stonehenge was built, between four and five thousand years ago. People who are long gone and left no written records brought the stones from miles away, carved them carefully, and set them in place. At various points, the site has been a graveyard, a site of animal sacrifice, a winter village. But one thing is certain: the intentional arrangement of the stones aligns meticulously to the sunrise of the summer solstice and the sunset of the winter solstice. The builders intended, at the very least, to capture the spectacles of the longest day and the longest night.

This year, about 8,000 people joined them in that spectacle. A party lasted through the night before, the grass field outside Salisbury filled with revelers in costumes. And at dawn on Wednesday morning, they all faced East, and watched the sun rise and cast the shadow of the Heel Stone directly into the center of Stonehenge.

“Stonehenge continues to captivate and to bring people together to celebrate the seasons, just as it has done for thousands of years,” said Nichola Tasker, director of Stonehenge at English Heritage, a charity that manages hundreds of historic sites.

“There was a wonderful atmosphere from sunset to sunrise, and everybody enjoyed a very atmospheric morning,” she added.

English Heritage also broadcast a livestream, and over 150,000 people tuned in from all corners of the world to watch the sunrise that marks the official start of summer.