Shortest period of daylight and longest night of the year.
"The solstice may have been a special moment of the annual cycle for some cultures even during Neolithic times. Astronomical events were often used to guide activities, such as the mating of animals, the sowing of crops and the monitoring of winter reserves of food. Many cultural mythologies and traditions are derived from this.
This is attested by physical remains in the layouts of late Neolithic and Bronze Age archaeological sites, such as Stonehenge in England and Newgrange in Ireland. The primary axes of both of these monuments seem to have been carefully aligned on a sight-line pointing to the winter solstice sunrise (Newgrange) and the winter solstice sunset (Stonehenge). It is significant that at Stonehenge the Great Trilithon was oriented outwards from the middle of the monument, i.e. its smooth flat face was turned towards the midwinter Sun."
I would 'figure, but do not know,
That Calanders and star charts could be devised or known by other means than a giant of a structure.
To my mind, (Which is uneducated on the subject)
It's value is one of meaning,
Symbolism, celebration, ceremony, whether cultural or religious.
Though I 'really can't imagine who's responsible for it,
A king, a spiritual leader, the people en masse,
Engaged by the idea of what they were to make?
Did all 'understand what they were making, and share together the same motivations,
A builder sometimes cares more for payment, than the use that is the clients interest.
But I'm rambling.
. . .
Art for arts sake, 'is a motivation often for people,
But I also think people create art for meaning,
Royal thrones or capital cities, decorated to show importance, prestige,
Places of worship or business,
Decorated, fine carved, to show the regard one holds.