Given such environmental and ecological settings, the area’s rough and difficult terrain has only a scant human population. Those groups that have adapted to it lead harsh lives. The Maasai, whose territory lies on both sides of the Tanzanian-Kenyan border, are the most numerous and best known ethnic group. Largely pastoral and semi-nomadic, the Maasai move their ephemeral settlements (small huts made of wood, mud and dung, plus acacia-branch enclosures where their cattle are kept safe) depending on the seasonal availability of water. The Batemi (or ‘Sonjo’ for the Maasai) are farmers who live in a small enclave in the middle of the vast Maasai territories. According to some sources this second ethnic group may be the descendants of those who peopled the prehistoric agricultural site of Engaruka to the south of Lake Natron.