(urth) Septimius Severus, Quadrifons

[Lee Berman]

Antonio Pedro Marques: 
>Septimius Severus's triumphal arch in Leptis Magna (Libya) is an arcus 
>quadrifons, i.e. a square with an arch in each side. I don't know whether 
>such arches were normal or rare; another one is one that is tought to have 
>been erected by Constantine, but for no known purposes.

Well, I don't know a lot about architecture but I remember the Arc de Triomphe 
in Paris being quadrifronic http://middlezonemusings.com/wp-content/uploads/2008/01/arc-de-triomphe.jpg
And it is based on the Arch of Titus, in Rome.  So, I'd guess it is a pretty 
standard form.
 
With regard to its significance in Short Sun, I think this blurb from Wikipedia
about Janus Quadrifrons might tie the reference to the concept of planetary and
universal destruction and rebirth which was introduced in BotNS.  Perhaps the 
Whorl is meant to show us a faster cycling version of the planets which, in turn, 
are faster cycling models of the universe.
 
>QUADRIFRONS:
 
>Quadrifrons is believed to be the fourth face of the God Janus and represents an 
>aspect of the God's attitude and life-cycle. Quadrifrons represents death and 
>destruction or the end of the life-cycle while Trifrons represents wisdom and 
>Bifrons represents virility thus completing the beginning-to-end cycle that 
>begins with Janus itself.