Far closer than her relations with Egypt were the ties which connected Babylonia with the great centre of civilization which lay upon her eastern frontier. In the course of this history reference has frequently been made to the contact which was continually taking place from the earliest historical period between Elam and the Sumerian and Semitic rulers of Sumer and Akkad. Such political relationships were naturally accompanied by close commercial intercourse, and the effects of Sumerian influence upon the native culture of Elam have been fully illustrated by the excavations conducted at Susa by the "Délégation en Perse."[22] Situated on the river Kerkha, Susa occupied an important strategic position at the head of the caravan routes which connected the Iranian plateau with the lower valley of the Tigris and Euphrates and the shores of the Persian Gulf. The river washed the foot of the low hills on which the town was built, and formed a natural defence against attack from the west. The situation of the city on the left bank of the stream is an indication that even in the earliest period its founders sought to protect themselves from the danger of sudden raids from the direction of Sumer and Akkad. The earliest Sumerian records also reflect the feelings of hostility to Elam which animated their writers. But from these scattered references it would appear that the Elamites at this time were generally the aggressors, and that they succeeded in keeping their country free from any political interference on the part of the more powerful among the Sumerian city-states. It was not until the period of Semitic expansion, under the later kingdom of Kish and the empire of Akkad, that the country became dominated by Babylonian influence.