these tribes , previously united only by distant ties of blood , mutually intelligible dialect , and certain shared customs and religious observances , most notable among these of course the practice of dragon-rebirth , first began to collaborate more closely for the joint administration of the elephant herds , which demanded more labour than could be organised by a single tribe ... . [ a ] centralisation further encouraged from the seventeenth century onwards by the increasing demand for ivory and gold , which penetrated to the african interior for several decades before the hunger for slaves was risen to a sufficient pitch to overcome the reluctance of the more aggressive slave-taking tribes to venture into dragon-territory ; and spurring , from the middle of the eighteenth century , the rapid development of gold-mining ( a venture that the tswana authorities indicate is most productively pursued through the co-operation of at least ten dragons , more than belong to nearly any individual tribe ) , and of the ivory trade , which by the open of the present century was sending some sixty thousand pounds a year to the coast without any suspicion on the part of the european traders , who carried the elephant teeth away , that these were obtained by , and not in despite of , the dragons who barred any further entry to the interior ... . on mosi oa tunya the falls at mosi oa tunya , so justly celebrated by all who have beheld them , were , despite their beauty , as a settlement inconvenient to men alone , who could not easily navigate the gorges , and in their natural state offered no real haven to feral dragons ; admired and occasionally visited , either for mere scenic pleasure or religious observation , they were yet undeveloped and uninhabited when the first sotho-tswana peoples moved into the region , and quickly made them their ceremonial capital , a further centralising tie among the tribes ... . [ t ] he desire of the dragon-ancestors for more comfortable shelter impelled the first attempts at cave-drilling , the relics of which may yet be seen at the falls , in the holiest and roughest chambers , low in the cliff-side ... and which later were to prove the foundation of the efficient gold-mining operations ... .