I just want to make a really small point here.
Francesca Rochberg in at least one of her books (I can find a reference if needed) mentions the connection between the observation of the rising of Sirius with the computation of the summer solstice, which occurs on the 15th day of the month. If we link signs to months, then we can consider that the middle of a sign/month corresponds to the cardinal points of the year.
There's another reference (again I'll find a reference if needed), in which it is postulated that from these cycles and knowledge of the 19 year return, that actually the Babylonians didn't observe solstices etc., but rather computed them.
Now I don't know from memory how far back all this is going or the timeline. I mention it more as a point which someone else, more knowledgeable on this, can take up if indeed it's even relevant.
But it may mean that knowing, at one point, the solstice occurred in the middle of the month, which is in turn linked to a sign, and that the Babylonians actually didn't observe solstices once they knew how to compute them, that the solstice was always meant to be understood as the middle of the fourth sign.
(I appreciate I don't have references, I can get them if needed but only if anyone is actually interested)
In addition, Martin Gansten made an interesting point recently:
http://skyscript.co.uk/forums/viewtopic.php?t=8679
Martin Gansten wrote:
(As an aside, the Greek fascination with this sort of pattern -- similar rising and setting times, etc -- predates the astrological use of the tropical zodiac, as reflected in one or two places in the Tetrabiblos, where it is clear that Ptolemy has taken over techniques originating in a zodiac that had the solstice/equinox points in the middle of their respective signs.)