If you just have a post, and mark how long it’s shadow is at noon every day(aka when it’s shortest each day) and you’re any distance at all from the equator, you’ll get a 365 day cycle of that length getting longer and shorter. Or you have a water clock made of a barrel with a leak, and time how long the days are, that’ll also give you that 365 day cycle, of days getting longer until they hit a maximum, then shorter until they hit a minimum, then longer until they hit that same maximum.