The Mongols were remarkably quick in transforming themselves from a purely nomadic tribal people into rulers of cities and states and in learning how to administer their vast empire. They readily adopted the system of administration of the conquered states, placing a handful of Mongols in the top positions but allowing former local officials to run everyday affairs. This clever system allowed them to control each city and province but also to be in touch with the population through their administrators. The seat of the Great Khanate in Dadu (Beijing) was the center of the empire, with all its pomp and ceremony, whereas the three semi-independent Central and western Asian domains of the Chaghatay, the Golden Horde, and the Ilkhanids were connected through an intricate network that crisscrossed the continent. Horses, once a reliable instrument of war and conquest, now made swift communication possible, carrying written messages through a relay system of stations. A letter sent by the emperor in Beijing and carried by an envoy wearing his paiza, or passport, could reach the Ilkhanid capital Tabriz, some 5,000 miles away, in about a month.