Xerxes I of Persia reigned until 465 BC. At the time, there was no standard system of measurement like there is today. No one wrote down exactly how tall he was. Historical records say that he was taller than the average man, which would suggest the 5'10" to 6'2" range.
By no means was he considered a giant from a height standpoint, although he certainly would have been large from a muscular-skeletal standpoint.