Police chiefs say they have planned for "all eventualities" ahead of the annual Summer Solstice celebrations at Stonehenge in Wiltshire.
Last year a record 36,500 revellers arrived for the event, causing traffic chaos and road closures.
Ch Supt Steve Hedley said: "If you want to enjoy Stonehenge and the Solstice, you are more than welcome. But it must be enjoyed peacefully."
Sunrise is at 0452 BST on Monday, with good weather predicted.
Last year there were 37 arrests for minor disorder and drugs offences.
A National Trust spokesman said the car park and camping areas are already full, although an overflow car park would be opened later on Sunday.