So-called “Classical” pieces were minted in large quantities beginning around 465 BCE, with embellishments to Athena’s Attic helmet and the addition of a crescent moon on the reverse.
After Athens’ defeat by Sparta in 404 BCE, Owl tetradrachms (sometimes referred to as Late Classical) were minted on a smaller planchet and are less sought after by collectors.
Beginning around 165 BCE, the “New Style” tetradrachms appeared with a wider, thinner planchet and changes on the reverse. The exact dating of all the styles (except some new-style Owls) remains a subject of debate. Dating by dealers and auction houses is frequently inconsistent.