Final answer:
Stonehenge is thought to have served as an ancient calendar and a site for ritualistic activities, indicated by its alignment with solar and lunar events and the presence of graves.
Step-by-step explanation:
Stonehenge has been interpreted as an ancient calendar due to its alignment with solar and lunar events, such as the summer and winter solstices. Carbon dating suggests construction took place between 2800 and 1500 BCE. The positioning of the stones indicates a strong relationship with the rising and setting of the Sun and Moon during critical times of the year, affirming its use for tracking celestial events.
Aside from being an astronomical tool, there is consensus among archaeologists that ritualistic activities were likely conducted at Stonehenge. The need for a large coordinated workforce and a dominant authority to orchestrate the construction hints at a complex society with religious or social gatherings. Moreover, multiple graves around the site's ditch suggest it had significant spiritual or ceremonial importance.
While some more fanciful theories, like involvement by aliens, have captured public imagination, these lack evidentiary support and are not considered plausible by the scientific community. The enormous effort required to build Stonehenge—quarrying and transporting stones up to 50 tons from distances as far as 450 miles—denotes a very organized society with the capability to undertake such an enduring task.