LONDON -- Thousands watched the sun glint over the horizon at Stonehenge on Thursday, celebrating the summer solstice at the Neolithic stone circle.

The sun rose behind the Heel Stone, which traditionally marks the spot on the horizon for the sunrise, at 4.52 a.m. Thursday (0352 GMT; 23:52 EDT Wednesday).

Crowds cheered and raised mobile phones for images as the rays flooded through the monument and announced the longest day of the year in the Northern Hemisphere.

Wiltshire Police estimated that 9,500 people attended and that 600 more celebrated at the nearby ancient monument in Avebury.

tweeted that it was the "perfect morning for the #SummerSolstice sunrise at Stonehenge."

The event passed peacefully. There were no arrests at Stonehenge, but two people were arrested at Avebury, one on suspicion of being drunk and disorderly and another on suspicion of driving while under the influence.

Stonehenge, which is believed to be 4,500 years old, is a World Heritage site known for its alignment with the movements of the sun. Thousands travel there to mark the solstices in summer and winter.