Stonehenge was built over 2000 years starting in 3000 BC. It was constructed in phases, with the first phase involving digging wells and erecting 80 standing stones known as blue stones that were brought from Wales. Later phases involved rebuilding the monument with larger sarsen stones weighing up to 30 tons brought from nearby. Archaeologists believe Stonehenge may have functioned as an astronomical observatory or religious site, and was part of a ritual landscape connecting it to other monuments.