Herodotus says that king Xerxes led his unprecedentedly huge forces and invaded Europe in 480 B C The size of the expeditionary force, including troops from Europe and non-combatants, was more than five million persons Other ancient sources agree that the great king's forces were vast in scale, but differ as to their number The German empire mobilized seven armies, i e, one million, five hundred thousand soldiers, on the western front at the beginning of the First World War The German troops were supplied, via thirteen railways, five-hundred-fifty trains a day Nevertheless, they were distressed by shortage of provisions Could the Persian empire, which had only primitive transport, maintain such huge forces for a long time and in a far distant country? Her transportation capability was meager It seems impossible that she mobilized and continued to supply such huge forces Modern historians doubt the size of the Persian forces which Herodotus gives They try to reduce his number to reasonable levels For that purpose they use two methods One is the philological method, used by many historians They criticize the texts and make known the organization of Xerxes' forces and the commanders' names There were three infantry divisions, three cavalry brigades, the Immortals, the guard troops and the non-combatants But, if one doubts about Herodotus' number, the size of the forces remains unknown The other method used employs logistics Gen Maurice and Gen v Fischer used this method They heed that the volume of provisions carried by the transport corps determined the scale of the forces This necessitates the fixing of some variables the mean speed, the size of the files, the carrying capability of pack animals and the rate of consumption of provisions What was the Persians' speed? It must have been that which reached the maximum value of the rate of flow There are some models for inquiring into the relation between the mean speed and the rate of flow I use Greenschields' model The outcome of my computation is that six parasangs a day is best, five a day next best and seven a day third best According to Xenophon's Anabasis, the Persians frequently marched six or seven parasangs a day When they crossed a bridge or river, their speed slowed Five parasangs a day was the usual speed So, I think that Xerxes' forces crossed the Hellespontos at the rate of five parasangs a day The rate of flow of animals was 500 4 heads/h, the rate of flow of infantrymen 1,429 7 persons/h What was the size of the Persian files? Gen v Fischer thought four files to be the usual size of the infantiy and two files that of the cavalry and transport corps I follow his view As the transport corps continued to cross for 7 days and nights, the total number of pack animals is 168,134 The transport corps carried 33,626,800 Ibs, consumed 31,945,460 Ibs, and could offer 1,681,340 Ibs to the combatants Such volume of provisions can maintain 41,000 infantrymen and 4,000 cavalrymen The number of an infantry division was 10,000 men, the number of cavalry brigade 1,000 men Xerxes' forces numbered 45,000 men Many historians think that the Persian fleet was far superior to the Greek Some believe in Herodotus' number, some modify his number to 1,000 or 800 or 600 Before the battle of Salamis, all Persian ships anchored in Phaleron bay I use this fact as a clue to estimating their scale I divide the length of the seashore by the width a trireme occupies in action The outcome is 300 ships The original fleet probably numbered about 400 ships My conclusion is that the land forces numbered 45,000 persons and the fleet 400 ships