their privileges and common interests. The most important unions were the Community of Saxons of Spiš () (later reduced and known as the Province of twenty-four Spiš towns), the Lower Hungarian Mining Towns (mining towns in Central Slovakia), Pentapolis (alliance of free royal towns in present-day Eastern Slovakia) and the Upper Hungarian Mining Towns (mining towns in eastern Slovakia including two mining towns in present-day Hungary). The inhabitants of the privileged towns were mainly of German origin, followed by Slovaks and smaller number of Hungarians. Royal privileges prove that several families of the developing local nobility (e.g., the Zathureczky, Pominorszky and Viszocsányi families) were of Slavic origin. The presence of Jews in several towns (e.g., in Bratislava, Pezinok) is also documented at least from the 13th century; the Jews' special status was confirmed by a charter of King Béla IV of Hungary in 1251, but decisions of local synods limited the participation of Jews (i.e., they could not hold offices and they could not own lands). The Muslims, living in the region of Nitra, also faced similar limitations; they disappeared (perhaps converted to Christianity) by the end of the 13th century. Period of the oligarchs (1290–1321) The last decades of the 13th century were characterized by discords within the royal family and among the several groups of the aristocracy. The decay of the royal power and the rise of some powerful aristocrats gave rise to the transformation of the administrative system: the counties that had been the basic units of the royal administration ("royal counties") transformed gradually into autonomous administrative units of the local nobility ("noble counties"); however, the local nobility was not able to stop the rise of oligarchs. Following the Mongol invasion of the kingdom, a competition started among the landowners: each of them endeavored to build a castle with or without the permission of the king. The competition started a process of differentiation among the noble families, because the nobles who were able to build a castle could also expand their influence over the neighbouring landowners. The conflicts among the members of the royal family also strengthened the power of the aristocrats (who sometimes received whole counties from the kings) and resulted in the formation of around eight huge territories (domains) in the kingdom, governed by powerful aristocrats in the 1290s. In present-day Slovakia, most of the castles were owned by two powerful aristocrats (Amade Aba and