As the author of the earliest secular account of the universe's formation, Anaximander of Miletus can lay a strong claim to the title of first Greek cosmologist. Tradition also credited him with invention of the first time-telling instruments: ‘He was the first to construct gnomons for the identification of solstices, time spans, horai and the equinox’ (οὗτος πρῶτος γνώμονας κατεσκεύασε πρὸς διάγνωσιν τροπῶν τε ἡλίου καὶ χρόνων καὶ ὡρῶν καὶ ἰσημερίας, Euseb. Praep. evang. 10.14.11). This paper reconstructs the location, design and function of a γνώμων which he erected at Sparta, and moots some intriguing parallels with the Augustan Horologium on the Campus Martius. Before we turn to the evidence, however, two points of terminology need to be clarified. The Greek term γνώμων can denote either a sundial—a pointer attached to a surface with marks for tracking its shadow—or the pointer itself, in English also called the gnomon; Eusebius’ reference to the identification of times suggests that what Anaximander created was in fact a sundial. Now, depending on its design, a sundial can tell either the hour of the day, the season of the year, or both; from Eusebius’ text it is not clear which function Anaximander's dial possessed, since the noun ὧραι can mean either ‘hours’ or ‘seasons’. But only one usage of the word would be appropriate for the sixth century: no authors refer to hours of the day prior to Herodotus (2.109) and there is no evidence for Greek sundials displaying hours prior to c.350 b.c.; by contrast, the use of ὥρα to mean ‘season of the year’ is as old as Homer and Hesiod, and the solstices and equinoxes mentioned by Eusebius demarcate the transitions between the seasons. Anaximander's device was a sundial, then, one which tracked seasons rather than hours. According to Diogenes Laertius, the cosmologist set up one such device at Sparta (2.1).