The development that separates the Late Preclassic from the early Classic period (300-900 AD) is the introduction of the Long Count calendar in the Petén lowlands and the development of a recognizable form of writing, which included phonetic glyphs. This appears to have taken place by the fourth century AD and marks the beginning of the greatest phase of Maya achievement.

During the Classic period all the cities we now know as ruined or restored sites were built, almost always over earlier structures. Elaborately carved stelae , bearing dates and emblem-glyphs, were erected at regular intervals. These tell of actual rulers and of historical events in their lives - battles, marriages, dynastic succession and so on. As these dates have come to be deciphered they have provided confirmation (or otherwise) of archeological evidence and offered a major insight into the nature of Maya dynastic rule.

Developments in the Maya area were still powerfully influenced by events to the north. The overbearing presence of the Olmecs was replaced by that of Teotihuacán , which dominated central Mexico during the Early Classic period. Armed merchants, called pochteca , operated at this time, spreading the influence of Teotihuacán as far as Petén and the Yucatán. They brought new styles of ceramics and alternative religious beliefs and perhaps preceded a complete military invasion. Whatever happened around 400 AD, the overwhelming power of Teotihuacán radically altered life in Maya lands. Influence spread south, via the Pacific coast, first to Kaminaljuyú on the site of modern Guatemala City and thence to Petén, where Tikal 's rise to power must have been helped by close links with Teotihuacán. Both cities prospered greatly: Kaminaljuyú was rebuilt in the style of Teotihuacán, and Tikal has a stela depicting a lord of Tikal on one side and a warrior from Teotihuacán on the other.

Exactly how the various centres related to one another is unclear, but it appears that large cities dominated specific regions though no city held sway throughout the Maya area. Broadly speaking, the culture was made up of a federation of city states, bound together by a coherent religion and culture and supporting a sophisticated trade network. The cities jostled for power and influence, a struggle that occasionally erupted into open warfare.

Intense wars were fought as rival cities sought to dominate one another, with no ruler appearing to gain ascendancy for very long. There were clearly three or four main centres that dominated the region through an uncertain process of alliance. Tikal was certainly a powerful city, but at one time Caracol in Belize defeated Tikal, as shown by a Caracol ball-court marker. Detailed carvings on wooden lintels and stone monuments depict elaborately costumed lords trampling on captives and spilling their own blood at propitious festivals, staged according to the dictates of the intricate and the precise Maya calendar. Copán and Quiriguá were certainly important centres in the southern area, while the cities of the highlands were still in their infancy.

At the height of Maya power, advances were temporarily halted by what is known as the Middle Classic Hiatus , a period during which there was little new building at Tikal and after which many smaller centres, once under the control of Tikal, became independent city states. The victory of Caracol over Tikal, some time around 550 AD, may have been a symptom or a cause of this, and certainly the collapse of Teotihuacán in the seventh century caused shock waves through all the civilizations of Mesoamerica. In the Maya cities no stelae commemorating events were erected, and monuments and statues were defaced and damaged. In all likelihood the Maya centres suffered revolts, and warfare raged as rival lords strove to win political power.

However, as the new kings established dynasties, now free of Teotihuacán's military or political control, the Maya cities flourished as never before. Architecture, astronomy and art reached degrees of sophistication unequalled by any other pre-Columbian society. Trade prospered and populations grew: Tikal had an estimated 40,000 people. Many Maya centres were larger than contemporary Western European cities, then in their "Dark Ages".

The prosperity and grandeur of the Late Classic (600-800 AD) reached all across the Maya lands: from Bonampak and Palenque in the west, to Labná, Sayil, Calakmul and Uxmal in the north, Altun Ha and Cerros in the east, and Copán and Quiriguá in the south, as well as hundreds of smaller centres. Masterpieces of painted pottery and carved jade (their most precious material) were created, often to be used as funerary offerings. Shell, bone and, rarely, marble were also exquisitely carved; temples were painted in brilliant colours, inside and out. Most of the pigments faded long ago, but vestiges remain, enabling experts to reconstruct vivid images of the appearance of the ancient cities.