Serbia until their social organization was destroyed by the Ottoman conquest, which would suggest that they came as slaves who had a change of 'ownership'. Historian Nicolae Iorga associated the Roma people's arrival with the 1241 Mongol invasion of Europe and considered their slavery as a vestige of that era, the Romanians taking the Roma from the Mongols as slaves and preserving their status. Other historians consider that they were enslaved while captured during the battles with the Tatars. The practice of enslaving prisoners may also have been taken from the Mongols. While it is possible that some Romani people were slaves or auxiliary troops of the Mongols or Tatars, the bulk of them came from south of the Danube at the end of the 14th century, some time after the foundation of Wallachia. The arrival of the Roma made slavery a widespread practice. Traditionally, Roma slaves were divided into three categories. The smallest was owned by the hospodars, and went by the Romanian-language name of țigani domnești ("Gypsies belonging to the lord"). The two other categories comprised țigani mănăstirești ("Gypsies belonging to the monasteries"), who were the property of Romanian Orthodox and Greek Orthodox monasteries, and țigani boierești ("Gypsies belonging to the boyars"), who were enslaved by the category of landowners. The abolition of slavery was carried out following a campaign by young revolutionaries who embraced the liberal ideas of the Enlightenment. The earliest law which freed a category of slaves was in March 1843, which transferred the control of the state slaves owned by the prison authority to the local authorities, leading to their sedentarizing and becoming peasants. During the Wallachian Revolution of 1848, the agenda of the Provisional Government included the emancipation (dezrobire) of the Roma as one of the main social demands. By the 1850s the movement gained support from almost the whole of Romanian society, and the law from February 1856 emancipated all slaves to the status of taxpayers (citizens). Geography With an area of approximately , Wallachia is situated north of the Danube (and of present-day Bulgaria), east of Serbia and south of the Southern Carpathians, and is traditionally divided between Muntenia in the east (as the political center, Muntenia is often understood as being synonymous with Wallachia), and Oltenia (a former banat) in the west. The division line between the two is the Olt River. Wallachia's traditional border with Moldavia coincided with the