In the first stage of the southward movement the Toltecs take the lead; it is stated that, being expelled from their own country, they came from the region of the north by both land and sea. Their chief center in their new land was Tollan, a pueblo which stands on a tributary of the Moctezuma River, a stream which falls into the Gulf of Mexico. This place seems to have been once a center of trade, for the Toltecs had the reputation of being clever craftsmen. In addition to knowledge of preparing skins and of manufacturing clothing and articles of domestic use, they must have become familiar with various metals and with the employment of stone for building. Colored stones and crystals were used in their decorative work; from the coasts were brought the colored shells with which they covered their buildings, and the feathers which were woven into their tapestry. Besides this, they had a reputation for the knowledge of medicinal plants. The ruins of Tollan are extensive; as described by those who saw some of the still extant buildings at the time of the Conquest, they must have been most impressive. Sahogun mentions especially the Chalchiauhapan (On the blue water) because it was built between the two forks of the river. There were richly decorated apartments, four being more magnificent than the rest. One was called the House of Gold, another the House of Green Jade and Turquoise; a third room was covered with colored sea-shells arranged as mosaics, the interstices being filled with silver; the last room was decorated in red stones, combined with colored shells. There were besides four rooms adorned with tapestry made of the plumage of different colored birds. As with Selinus, a famous Greek city in Sicily, the downfall of Tollan must have been sudden, for there was an unfinished building seen in the ruins with remarkable pillars in the form of rattlesnakes, and also a mound in process of construction to be used as a foundation of a building of unusually large size. This fate seems to have overtaken it some centuries before the Spanish conquest, and was probably due to an insurrection among the subordinate pueblos.