in km. These are fortifications that were used not to protect a specific city or town, but a large territory. Examples include the Great Wall of China. Provide an estimate in km of the extent of the longest of such fortification systems. If not present, enter '0'. Very large circular walls protecting a settlement are not long walls - long walls are fairly linear and protect whole areas from incursions. If a polity inherits a stone wall from a previous one and continues to use and repair it, then we should probably code it as present.