What prehistoric monument in Wiltshire, England dates to around 2500 BC?

The prehistoric monument in Wiltshire, England, associated with around 2500 BC is Stonehenge. It stands on Salisbury Plain near Amesbury and was built in multiple phases over more than a thousand years.

The earliest earthwork at the site dates to about 3100 BC. The famous arrangement of large sarsen stones was erected mainly between about 2600 and 2400 BC, while construction and rearrangement continued until roughly 1600 BC. The monument includes massive uprights joined by horizontal lintels using sophisticated mortise-and-tenon joints.

Stonehenge's builders also used bluestones transported from the Preseli Hills in modern-day Wales, around 150 miles away. The monument is aligned with important solar events: the sunrise at the summer solstice and sunset at the winter solstice. Its original purpose remains uncertain, with evidence suggesting ceremonial, funerary, and astronomical roles.

Newgrange, Carnac, and Avebury are also prehistoric monuments, but none is the single landmark described by this question. Avebury is in the same broader Wiltshire landscape and is therefore the most likely source of confusion.