The numbers of troops that Xerxes mustered for the second invasion of Greece have been the subject of endless dispute, because the numbers given in ancient sources are very large indeed. Herodotus claimed that there were, in total, 2.5 million military personnel, accompanied by an equivalent number of support personnel.[28] The poet Simonides, who was a contemporary, talks of four million; Ctesias, based on Persian records, gave 800,000 as the total number of the army (without the support personnel) that was assembled by Xerxes.[29] While it has been suggested that Herodotus or his sources had access to official Persian Empire records of the forces involved in the expedition, modern scholars tend to reject these figures based on knowledge of the Persian military systems, their logistical capabilities, the Greek countryside, and supplies available along the army's route.[30]