Wolfgang Helbig (1909) suggested that the phalanx had an overall gradual development. he developed this theory from evidence of old archaic poets. With which he concludes that the Euboians and not the spartans had actaully invented the phalanx battle technique. Helbig also took a look at the Chigi Olpe (6th or 5th century) which is the earliest depiction of the Hoplite phalanx. He also believed that in order for this to work they used the Porpax shield because it is only effective in close order formations. So once the Greeks had the Porpax shield in their repertoire they had the Hoplite Phalanx.