The priests instructed the younger sons of the ruling family as well as their own, in the priestly duties and learning; in the computation of years, months, and days; in unlucky times; in fetes and ceremonies; in the administration of the sacraments; in the practices of prophecy and divination; in treating the sick; in their ancient history; and finally in the art of reading and writing their hieroglyphics, which was taught only to those of high degree. Genealogies were carefully preserved, the term meaning "of noble birth" being _ah kaba_, "he who has a name." The elaborate attention given to the subject of lineage, and the exclusive right of the _ah kaba_ to the benefits of education, show that in the northern part of the Maya territory at least government rested on the principle of hereditary succession. The accounts of native as well as of Spanish writers leave the impression that a system not unlike a modified form of feudalism prevailed. [Illustration: DIAGRAM SHOWING PERIODS OF OCCUPANCY OF PRINCIPAL SOUTHERN CITIES] {15} In attempting to gain an approximate understanding of the form of government which existed in the southern part of the Maya territory it is necessary in the absence of all documentary information to interpret the southern chronology, architecture, and sculpture--practically all that remains of the older culture--in the light of the known conditions in the north. The chronology of the several southern cities (see pl. 2) indicates that many of them were contemporaneous, and that a few, namely, Tikal, Naranjo, Palenque, and Copan were occupied approximately 200 years, a much longer period than any of the others.[15] These four would seem to have been centers of population for a long time, and at least three of them, Tikal, Palenque, and Copan, attained considerable size. Indeed they may well have been, like Chichen Itza, Uxmal, and Mayapan, at a later epoch in the north, the seats of halach uincil, or overlords, to whom all the surrounding chiefs were tributary. Geographically considered, the country was well apportioned among these cities: Tikal dominating the north, Palenque, the west, and Copan, the south.