More than 30,000 people are expected to descend on Stonehenge to attend this year's summer solstice.
Several thousand more – including hippies and pagans – are likely to visit the nearby Avebury stone circle to witness the sun rising on the longest day.
Last year an estimated 36,000 people attended and this year a similar number are expected to join in celebrations.
Wiltshire Police said sunrise would be at 4.52am and officers warned that illegally parked vehicles would be "dealt with appropriately".
A number of road closures are also in place and revellers are urged to use public transport to get to the world famous monument.
Stonehenge is believed to have been used as an important religious site by early Britons 4,000 years ago. Recent pagan celebrations at the site began in the 20th Century
Superintendent Gavin Williams, who is leading the policing operation, said: "We will be managing a proportionate policing operation at both Stonehenge and Avebury and will be policing in the same way we would any night time economy.
"As always, we have been working closely with our partners to make sure that the right conditions of entry are in place.
"This year falls on Saturday so we are expecting in the region of 30,000 visitors throughout the night. The police will be there to ensure public safety and support the event.
"There will be drugs dogs and amnesty bins at the entry points and we will deal robustly with any disorder or anti-social behaviour.
"The best advice we can give to the public is to use the bus service provided and to check the conditions of entry before attending the event or you may not be allowed in.
"Only moderate consumption of alcohol is permitted and therefore you could be turned away.
"We want everyone at Solstice to have a safe event this coming weekend."
More than a million people flock to Stonehenge every year, with thousands attending ceremonies to mark the solstices in summer and winter.