The development of serfdom, which was made official in Russia by the Ulozhenie [Law Code] of 1649, took place as the state began to centralize under the grand princes of Moscow. Noblemen and clergymen received land grants from the tsar in return for protecting his interests and security. Peasant labor became vital to the existence of this land-owning class. Thus, peasant migration was at first restricted to two weeks per year, and then only to the time around St. George’s Day (Iurev Den') at the end of the harvest, and then forbidden altogether. Finally, the Ulozhenie deprived the serfs of personal rights, and essentially bound them to the landowners.