In today's Nature: Archeologists reconstruct from a century-old find a 2100-year-old version of Posidonius' astronomical calculator, described by Cicero as accurately reproducing the movements of the sun, moon, and planets in the sky, and thought until now to be a myth. The 37-gear mechanism is more complicated than anything Christian society devised for over 1700 years, and suggests that the ancient Greeks might have had primitive computers capable of doing arithmetic. [Also: Times UK; LA Times; Java animation]