Protected by difficult terrain and heavy vegetation, the ruins of few ancient Maya cities were known before the 19th century, when explorers and archaeologists began to rediscover them. The age and proliferation of Maya writings have been recognized since about 1900, when the calendrical content of Maya hieroglyphic inscriptions was deciphered and the dates correlated with the Christian calendar. For most of the 20th century, only the extensive calendrical data of Maya inscriptions could be read, and as a result, Maya scholars hypothesized that the inscriptions were pure calendrical records. Because little evidence of warfare had been recognized archaeologically, the Classic Maya were thought of as peaceful timekeepers and skywatchers. Their cities, it was thought, were ceremonial centers for ascetic priests, and their artwork anonymous, without concern for specific individuals.
More recent scholarship changes the picture dramatically.
In 1958 Heinrich Berlin demonstrated that certain Maya hieroglyphs, which he called emblem glyphs, contained main signs that varied according to location, indicating dynastic lines or place names. In 1960, Tatiana Proskouriakoff showed that the patterns of dates were markers of the important events in rulers' lives. The chronological record turned out to serve history and the perpetuation of the memory of great nobles. With these elements the Maya built ranging palaces, pyramids, shrines, and even ballcourts. Maya builders frequently set a new structure directly over an old one, and within ranging palace complexes, doorways were frequently walled up and changed.