Triskelion
The Spiral of Life
Newgrange's tri-spiral dates to a tomb built around 3200 BC; knowth.com places it 'at least 2500 years before the Celts reached Ireland'.
knowth.com, 'Newgrange', on orthostat C10 and the tomb's construction around 3200 BC
Three spirals or three bent legs radiating from a common centre.
More context
The triskelion, or triskele, is a figure of three spirals or three bent limbs radiating from one centre. A triple spiral is carved on orthostat C10 in the chamber of the Newgrange passage tomb, built around 3200 BC. Spiral triskeles recur in Iron Age La Tène art. The name is Greek for 'three-legged'. It properly belongs to the emblem of three running legs on Greek coins, among them Sicily's under Agathocles, and later to the arms of the Isle of Man. No reading survives from its Newgrange builders or La Tène smiths.
Light
One of Europe's oldest surviving designs, carved at Newgrange around 3200 BC, and still on the flags of Sicily and the Isle of Man.
Shadow
Labelled Celtic, it is made to stand for a people who did not yet exist when it was carved, and its spiritual meanings are modern.