Byzantium in the 3rd millennium BCC Anatolia and Thrace developed the most advanced architecture in the world during the Bronze Age. The first true cities grew along the Dardanelle and Adrian Rivers. Byzantine masonry came into full development by 2900bc, with the growing trade routes and prosperity of the northern civilization. Urbanization led to the construction of strong, fortified cities and the design of sophisticated buildings, tall to resist the bitter northern winters. By 2700bc they were in contact with the Iroquois civilization. In 2230bc, Byzantine freebooters, out searching for new sources of stone and marble, plundered the Kazakh tribes east of Iroquoia. By 2150bc, Byzantine warriors had adapted the fighting techniques of the Celts while a trickle of crafts trade transpired between Thrace and Gaul.