It was a natural phenomenon, this periodic rise at intervals of little more than a century, of ascetic creeds in Central Arabia. Always the votaries found their neighbours’ beliefs cluttered with inessential things, which became impious in the hot imagination of their preachers. Again and again they had arisen, had taken possession, soul and body, of the tribes, and had dashed themselves to pieces on the urban Semites, merchants and concupiscent men of the world. About their comfortable possessions the new creeds ebbed and flowed like the tides or the changing seasons, each movement with the seeds of early death in its excess of rightness. Doubtless they must recur so long as the causes⁠—sun, moon, wind, acting in the emptiness of open spaces, weigh without check on the unhurried and uncumbered minds of the desert-dwellers.