In the 18th century, a reform of the administrative division of the principalities of Moldova and Wallachia was carried out, introducing subdivisions of the counties (judeţe). This reform was carried out undervoivodeConstantin Mavrocordat first in 1740 in Wallachia and subsequently in 1741 in Moldavia. The subdivisions followed the example of applied by Austria during its occupation of Oltenia. 
The new subdivisions of the counties were:
Plai, a subdivision, used only in Wallachia, including the villages in the moutain area. A plai was directed by a vâtaf de plai whose responsibilities included the supervision of the northern border of the principalities, the apprehension of delincvents and of fugitive tax-evaders, the collection of taxes from the inhabitants of the plai (called plăieşi), judging minor disputes between locals and nominating the pârcălabi (mayors) of the villages of the plai. The position of vătaf de plai was considered important and therefore they were appointed directly by the voivode. Their payment followed the traditions of the country: the were exempted from paying taxes, they were entitled of several days of compulsory service by the plăieşi and also received payment in kind from them.
Plasa used for the plain areas of Wallachia and Ocolul for the entire territory of Moldavia was another type of subdivision of the counties. They were directed by the zapcii de plasă in Wallachia and he ocolaşi in Moldavia, who were appointed by the ispravnici and had similar responsibilities in both countries. They were supposed to implement the orders of the ispravnici, and to collect taxes. Though in principle they were not empowered to judge conflicts, they often did so with the authorization and complicity of the ispravnici, The main difference between them and the vătafi de plai was that both the zapcii and the ocolaşi received salaries.
The division of counties was unified under Carol I, all counties being divided into plăși. Each plasă was headed by a Pretor, appointed by the county Prefect. The institution headed by the Pretor was called Pretură. After World War I, the system was extended also to the new annexed territories. In 1938, the country's 71 judeţe were divided into 429 plăşi.
The system was modified in 1950 by introducing raions, following the Soviet system.
^Organizarea de stat Tarilor Romane in secolul fanariot 
^"Legea nr. 5 pentru raionarea administrativ-economică a teritoriului Republicii Populare Romîne" (published in Buletinul Oficial, No. 77 / September 8, 1950); Ronald A. Helin, "The Volatile Administrative Map of Rumania", in Annals of the Association of American Geographers, Vol. 57, No. 3 (September 1967), pp.481-502