Farmers and herders settled in the plains surrounding the Hindu Kush as early as 7000 B.C. These people may have grown rich off the lapis lazuli they found along riverbeds, which they traded to early city sites to the west, across the Iranian plateau and Mesopotamia. As farms and villages grew and thrived in Afghanistan, these ancient people eventually invented irrigation (digging ditches for water so it flows to crops) that allowed them to grow crops on the northern Afghanistan desert plains. This civilization (advanced state of organization) is today called BMAC (Bactria–Margiana Archaeological Complex), or the "Oxus civilization".