Nine people were arrested as thousands gathered at the prehistoric stone circle in Stonehenge to mark the longest day of the year, British police said Sunday.

Around 23,000 people, some with flowers in their hair and playing drums and accordions, showed up at the site in Wiltshire, southwest England to see the sun rise at 4:52am (0352 GMT). The main stones at Stonehenge, a World Heritage Site, are thought to have been erected in around 2500 BC.

Thousands of people including modern-day druids flock to the site every year to celebrate the solstice, which is also the official start of summer. The sun rises in alignment with some of the main stones at the monument and experts believe that Stonehenge was built as a prehistoric temple.

Attendance was down on the 36,000 who went to Stonehenge for last year’s summer solstice. Superintendent Gavin Williams, who led police at the scene, said nine people had been arrested, mainly over alleged drug offences, a lower figure than in previous years.

“Solstice 2015 has been a great success with approximately 23,000 people celebrating at Stonehenge in the positive, friendly atmosphere as they waited for the sunrise,” he added. “This year the crowds were able to see the sun as it appeared over the horizon, before it disappeared under low cloud.”