Sundials in antiquity

Sundials were well known in antiquity.  This first-century Roman mosaic from Pompeii, Plato’s Academy meets in the groves outside Athens (depicted in the upper right corner).  Behind them, beside a sacred doorway and a tree, is a votive column headed by a sundial.

Image. Plato's Academy, Roman mosaic from Pompeii, now at the Museo Nazionale Archeologico, Naples, Inventory no. 124545. Date: 1st century CE. Dimensions: Height: 86 cm (33.9 in). Width: 85 cm (33.5 in). Source: Photo by Jebulon, 29 July 2015. Wikimedia (Public domain).

Resources. 

The HSM Oxford possesses a Roman vertical disc sundial, one of only a handful of portable sundials to survive from antiquity: Inv. no. 51358.

Animated explanations of a wide range of Greek sundials can be found here.