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. Some scholars argue that the feudal lords tried to legally tie down the peasants to their land. Certain categories of feudally dependent peasants, such as davniye lyudi (давние люди), polovniki (половники), poruchniki (поручники), dolzhniki (должники), were deprived of the right to leave their masters. The boyars and monasteries also tried to restrict other categories of peasants from switching their feudal lords. However, until the late 16th century peasants could leave their land in the weeks preceding and coming after St. George's day in the autumn. Marxist scholars (e.g., Aleksandr Khoroshev) often spoke of class struggle in Novgorod. There were some 80 major uprisings in the republic, which often turned into armed rebellions. The most notable among these took place in 1136, 1207, 1228–29, 1270, 1418, and 1446–47. The extent to which these were based on "class struggle" is unclear. Many were between various boyar factions or, if a revolt did involve the peasants or tradesmen against the boyars, it did not consist of the peasants wanting to overthrow the existing social order, but was more often than not a demand for better rule on the part of the ruling class. There did not seem to be a sense that the office of prince should be abolished or that the peasants should be allowed to run the city. Throughout the republican period, the archbishop of Novgorod was the head of the Orthodox church. The Finnic population of the Novgorod land was undergoing Christianisation. The sect of Strigolniki spread to Novgorod from Pskov in the middle of 14th century, its members renouncing ecclesiastic hierarchy, monasticism and sacraments of priesthood, communion, repentance and baptism. Another sect, called the heresy of the Judaizers by its opponents appeared in Novgorod in the second half of 15th century