Stonehenge

Between 2600 BC and 2400 BC, Stonehenge hosted religious festivals attended by up to 4,000 people.

An excerpt from the article 16 facts about Stonehenge
The festivals, including animal sacrifices, coincided with the winter and summer solstices. Since sacrificial animals were transported from distant regions, such as the highlands of Scotland, it led to a theory that Stonehenge may have been the center of the unification of the inhabitants of the British Isles.