Despite Herodotus's attribution of the invention of the sundial to the Babylonians in 430 BCE, the earliest known sundials were simple gnomons of Egyptian origin invented around 3500 BCE. More complex devices were developed over time, the earliest surviving one is a limestone sundial that dates back to 1500 BCE, discovered in the Valley of the Kings in 2013.[3] It was found in a housing area of construction workers and its division of daytime into 12 parts was possibly used to measure work hours.[3] Shadow clocks were modified sundials that allowed for greater precision in determining the time of day, and were first used around 1500 BCE.[1] Their major innovation was a modified, more precise gnomon that allowed for the division of night time into 50 parts, with an additional two "twilight hours" in the morning and evening. The shadow clock gnomon was made up of a long stem divided into six parts, as well as an elevated crossbar that cast a shadow over the marks.