Sentence:  Saturn has supplied to the Greeks and Romans the source of a beautiful personification; they have represented him as Time, ... thus with his scythe is he considered to cut down in endless succession every ripened race of man; and as the serpent is annually renewed by the cast of its skin, so is every falling race of man held to be renewed by a young and succeeding progeny; from hence arose the fiction, that Saturn devoured his own children, and hence also is the continuous <WSD>cirque</WSD> of imposts at Stonehenge an apt representation of this well imagined emblem. 
Meaning of the word marked with <WSD> tags:  Something in the shape of a circle or ring, such as a Roman circus.