Aztec rulers, Mexica and others, used their authority to develop, expand, and defend the Excan tlatoloyan and other confederations in or near the Basin of Mexico. That region contained about sixty political units, each called an altepetl. The largest, most militarily and economically powerful was Tenochtitlan, the Mexica capital city. The most common translations, city-state or kingdom, capture something essential. They had urban cores, and they were each ruled by supreme rulers, the tlatoani. As important as the altepetl was, localities that constituted them, known as tlaxilacalli or calpolli, smaller units that in many ways constituted communities unto themselves, were also important. Violence was a key part of Aztec political culture and state and confederation building in the late Postclassic period. War practices relied upon structure and discipline, weaponry, the pursuit of captives, and the vanquishing of enemies who produced material wealth in the form of everyday and luxury items paid as tribute to the imperial powers. Whether through elite marriages or wars, inter-altepetl relations took place within a context in which the Excan tlatoloyan sought aggressively to enlarge its domain of control by becoming an expansive confederation that can be considered a hegemonic empire.