But gifts and care were not enough. Treachery to his friends was still to be feared from such a god. He must still further be bought off; everything that to an Indian seemed valuable was proffered to the Indian's god, to keep him in good humor. And since human life was the most precious thing an Indian could understand, it became his most important and finally his most frequent offering. To the Indian it seemed no crime to take a life to please a god. He had no idea of retribution after death, and he came to look upon human sacrifice as a legitimate, moral, and even divine institution. In time, such sacrifices became of almost daily occurrence at each of the numberless temples. It was the most valued form of worship; so great was its importance that the officials or priests had to go through a more onerous training than does any minister of a Christian faith. They could reach their position only by pledging and keeping up unceasing and awful self-deprivation and self-mutilation. Human lives were offered not only to one or two principal idols of each community, but each town had also many minor fetiches to which such sacrifices were made on stated occasions. So fixed was the custom of sacrifice, and so proper was it deemed, that when Cortez came to Cempohual the natives could think of no other way to welcome him with sufficient honor, and in perfect cordiality proposed to offer up human sacrifices to him. It is hardly necessary to add that Cortez sternly declined this pledge of hospitality. These rites were mostly performed on the teocallis, or sacrificial mounds, of which there were one or more in every Indian town. These were huge artificial mounds of earth, built in the shape of truncated pyramids, and faced all over with stone. They were from fifty to two hundred feet high, and sometimes many hundreds of feet square at the base. Upon the flat top of the pyramid stood a small tower,--the dingy chapel which enclosed the idol. The grotesque face of the stone deity looked down upon a cylindrical stone which had a bowl-like cavity in the top,--the altar, or sacrificial stone. This was generally carved also, and sometimes with remarkable skill and detail. The famous so-called "Aztec Calendar Stone" in the National Museum of Mexico, which once gave rise to so many wild speculations, is merely one of these sacrificial altars, dating from before Columbus. It is a wonderful piece of Indian stone-carving.