Law") of 1649 gave serfs to estates, and in 1658, flight was made a criminal offense. Russian landowners eventually gained almost unlimited ownership over Russian serfs. The landowner could transfer the serf without land to another landowner while keeping the serf's personal property and family; however, the landowner had no right to kill the serf. About four-fifths of Russian peasants were serfs according to the censuses of 1678 and 1719; free peasants remained only in the north and north-east of the country. Most of the dvoryane (nobles) were content with the long time frame for search of the runaway peasants. The major landowners of the country, however, together with the dvoryane of the south, were interested in a short-term persecution due to the fact that many runaways would usually flee to the southern parts of Russia. During the first half of the 17th century the dvoryane sent their collective petitions (, ) to the authorities, asking for the extension of the "fixed years". In 1642, the Russian government established a 10-year limit for search of the runaways and 15-year limit for search for peasants taken away by their new owners. The Sobornoye Ulozhenie introduced an open-ended search for those on the run, meaning that all of the peasants who had fled from their masters after the census of 1626 or 1646–1647 had to be returned. The government would still introduce new time frames and grounds for search of the runaways after 1649, which applied to the peasants who had fled to the outlying districts of the country, such as regions along the border abatises called () (ukases of 1653 and 1656), Siberia (ukases of 1671, 1683 and 1700), Don (1698) etc. The dvoryane constantly demanded that the search for the runaways be sponsored by the government. The legislation of the second half of the 17th century paid much attention to the means of punishment of the runaways. Serfdom was hardly efficient; serfs and nobles had little incentive to improve the land. However, it was politically effective. Nobles rarely challenged the tsar for fear of provoking a peasant uprising. Serfs were often given lifelong tenancy on their plots, so they tended to be conservative as well. The serfs took little part in uprisings against the empire as a whole; it was the Cossacks and nomads who rebelled initially and recruited serfs into rebel armies. But many landowners died during serf uprisings