More than a half of all Novgorodian privately owned lands had been concentrated in the hands of some 30–40 noble boyar families by the 14th–15th century. These vast estates served as material resources, which secured political supremacy of the boyars. The House of Holy Wisdom (Дом святой Софии, "Dom Svyatoy Sofiy") — the main ecclesiastic establishment of Novgorod — was their chief rival in terms of landownership. Its votchinas were located in the most economically developed regions of the Novgorod Land. The Yuriev Monastery, Arkazhsky Monastery, Antoniev Monastery and some other privileged monasteries are known to have been big landowners. There were also the so-called "zhityi lyudi" (житьи люди), who owned less land than the boyars, and unprivileged small votchina owners called "svoyezemtsy" (своеземцы, or private landowners). The most common form of labor exploitation — the system of metayage — was typical for the afore-mentioned categories of landowners. Their household economies were mostly serviced by slaves (kholopy), whose number had been constantly decreasing. Along with the metayage, monetary payments also gained significant importance by the 2nd half of the 15th century.