On the very interesting Time Team archaeology programme they once visited a Mediterranean island (one of the Balearics, I think, or maybe Malta) to dig an ancient enclosure. They discovered that its entrance was aligned to the Southern Cross, visible at the time of building as it crossed the meridian, just above the horizon, at certain times of the year. Due to the precession of the equinoxes, it is not now visible this far north. it would be interesting to know if the builders actually saw it as a cross, as there is no central star (as in Cygnus) or in some other way - an aperture, maybe.

Penny