Forced to retire ever farther inland to more inaccessible regions, the unruly tribes, who lived by pillage, rapine, and the slave traffic, were a perpetual menace and a source of grave danger to the peaceful native population of the interior, who rightly claimed France's protection as the price of their loyalty. To reach these raiders and to inflict upon them losses to inspire them with a wholesome fear of French arms was no easy task, and before it could be accomplished the thirsty sands of the sun-scorched desert drank deep of the noblest blood of France. More difficult still, even if less brilliant than the soldier's, was the engineer's task, which was to render definite, beneficial, and profitable such land as the sword had conquered.