I'm kicking myself for not linking to Judith Weingarten's blog post, Time Gazing at the Pantheon in Rome yesterday. It's good explanation of how the Emperor could have used the Pantheon and it's readably short. The only quibble I have is the use of the word sundial. Sundials come in all sorts of shapes, but some shapes are much better suited to being a sundial than others. In the case of the Pantheon in Rome, it's staggeringly well suited to being a sundial. If you wanted to easily create an accurate timekeeper then the Pantheon is the sort of thing you'd want.

A while back there was a news story that the Pantheon may have been constructed to create a special effect in the sunlight at the equinoxes. I'm slow in reacting because I've read the book where the claim appears, and I've been taking time to try and track down one or two other ideas regarding the Pantheon. The story is based on a chapter from a new book Time in Antiquity by Robert Hannah, and it's a great example of how thinking about ancient astronomy has gently expanded over the past decade.