<P> Sumerian cities were surrounded by defensive walls . The Sumerians engaged in siege warfare between their cities, but the mudbrick walls were able to deter some foes . </P> <P> Examples of Sumerian technology include: the wheel, cuneiform script, arithmetic and geometry, irrigation systems, Sumerian boats, lunisolar calendar, bronze, leather, saws, chisels, hammers, braces, bits, nails, pins, rings, hoes, axes, knives, lancepoints, arrowheads, swords, glue, daggers, waterskins, bags, harnesses, armor, quivers, war chariots, scabbards, boots, sandals, harpoons and beer . The Sumerians had three main types of boats: </P> <Ul> <Li> clinker - built sailboats stitched together with hair, featuring bitumen waterproofing </Li> <Li> skin boats constructed from animal skins and reeds </Li> <Li> wooden - oared ships, sometimes pulled upstream by people and animals walking along the nearby banks </Li> </Ul> <Li> clinker - built sailboats stitched together with hair, featuring bitumen waterproofing </Li>

What happened to the sumerian states as they expanded