Petru or Petre: first names still divide the lands Romania was made from

Wallachia and Moldavia united in 1859; Transylvania joined in 1918. Of the 9,293 people called Petru in the trade register, 3 in 100 live in Wallachia (Muntenia and Oltenia), home to 28 in 100 of everyone in the register. There the same name, Peter, is written Petre. Type a first name and see where it is at home.

The map counts people and shows no one: no surnames, no addresses. Communes with fewer than five bearers are folded into their county’s total.

Two lands

Wallachia writes first names differently from the rest of Romania#

A few dozen first names come in two forms, and the choice depends on the place: Petru or Petre (Peter), Ioan or Ion (John), Neculai or Nicolae (Nicholas). The map adds them all into one score. Blue communes choose the forms of Moldavia, orange ones the forms of Wallachia.

The score was fitted on 18 counties only: 12 in Wallachia and six in Moldavia. The other 24 counties were left out of the calculation. Each falls on the side of the historic land it belonged to: all 16 counties of Transylvania, Banat, Crișana and Maramureș, plus Galați and Vrancea, come out blue; Buzău, Brăila, Ilfov and Bucharest come out orange. Dobruja, which belonged to neither principality, writes first names as Wallachia does.

Pairs

Ioan, Toader, Neculai: each pair has its own map#

Ioan and Ion. In Gorj and Argeș, 8 in 100 bearers of the pair are Ioan; in Cluj, 93; in Bihor, 97. In Moldavia Ioan leads more narrowly: 77 in Iași. Bucharest, where people moved from all over the country, is half and half: 45.

Toader and Tudor (both Theodore). Here the map splits differently. Toader is the form of Moldavia (85 in 100 bearers of the pair in Vrancea, 77 in Galați) and of northern Transylvania (66 in Bistrița-Năsăud, 50 in Maramureș). In Cluj only 4 in 100 are Toader, in Bihor 3. Iași is the exception in Moldavia: 22.

Neculai and Nicolae. Neculai belongs mostly to Moldavia: 73 in 100 people with the name live there. Niculae, a third form, belongs to Muntenia: 53 in 100.

Five groups

From first names alone, a calculation finds the three lands again#

Every commune with at least 150 people in the register has a profile: how often its 400 most common first names appear there, compared with the national average. A clustering algorithm split 1,440 such communes into five groups without knowing where any of them lies.

On the map, the groups follow the historic lands closely. 94 in 100 communes land in the group of their own land. Five groups drawn by distance alone, without names, reach 89, because nearby places are alike anyway. The difference shows near the old borders: for the 122 communes within 25 km of a commune of another land, names get 77 in 100 right and distance 55.

The fourth group is made of Transylvanian communes where Hungarian first names lead (István, Zoltán, Csaba). The fifth is small and mixed. A few communes fall outside the pattern, mostly in Brașov, Caraș-Severin, Vrancea, Maramureș and Sibiu; why is not established here.

Where it changes

Across the Carpathians and across the Siret, first names change abruptly#

The score jumps most where an old border ran. Between neighbouring communes of Prahova and Brașov, on either side of the Carpathians, the jump is +0.68. Between Brăila and Galați, on either side of the Siret, +0.55: in Brăila county, 32 in 100 bearers of the pair are Petru; in Galați, 85.

Lines between counties of the same land change little: Argeș and Dâmbovița +0.05, Bacău and Neamț +0.01, Vaslui and Iași +0.03. The Teleorman–Olt line, which follows the river Olt, the old divide between Muntenia and Oltenia, shows a small jump too: +0.24.

Communes touching across the line between two counties; the difference in mean score. The score runs from about −1.3 (Teleorman) to +1 (Botoșani).
Between counties	Old border	Jump in score	9 in 10 resamples
Prahova – Brașov	the Carpathians	+0.68	+0.46 … +0.86
Brăila – Galați	the Siret	+0.55	+0.18 … +0.78
Buzău – Vrancea	the Milcov, then 1968	+0.53	+0.19 … +0.84
Argeș – Dâmbovița	—	+0.05	−0.07 … +0.18
Bacău – Neamț	—	+0.01	−0.14 … +0.18
Vaslui – Iași	—	+0.03	−0.17 … +0.18
Buzău – Prahova	—	−0.14	−0.27 … +0.03
Ialomița – Călărași	—	−0.15	−0.26 … +0.06
Bacău – Vrancea	—	−0.14	−0.33 … +0.08

The Milcov

On the Milcov, the change spreads over a band about 15 km wide#

Until 1862 the Milcov river divided Moldavia from Wallachia and cut the town of Focșani in two. The dotted line is the 1856 border, traced from the Austrian military survey. Communes within 10 km of it differ by +0.34 between the two banks.

The jump does not sit on the line itself. The same comparison made on 41 parallel lines, shifted two kilometres at a time north or south, ranks the true border only third of 41: the change happens across a band about 15 km wide around it. Focșani, the town the border split, scores 0.09, close to the middle.

A newer border shows too. In Vrancea, the communes south of the old border, once Wallachian, write first names more like Moldavia than their neighbours in Buzău, though in 1930 almost all the communes on both sides of this line (18 of 19) belonged to one county, Râmnicu Sărat. The jump on the Buzău–Vrancea line drawn in 1968: +0.32. Inside Vrancea, between the south and the north of the old border: +0.36.

The jump in score on the true line (the bar at 0 km) and on parallel lines shifted south (minus) or north (plus).

What the map counts

People in the trade register, at their firm’s address#

The data come from the trade register: 1,198,955 people who have or had a business in their own name, as a sole trader or a family business. They are adults, not the whole population, and the place is the commune of the registered address, not of birth.

Names are written as on identity papers. Someone listed as Ioan may be called Ion at home. Each person counts once for every first name they carry.

How the map was made#

The ONRC register of 19 October 2026 was parsed with the same code as the page Numele bunicilor: natural persons (sole traders and family businesses), each with surname, first names and the commune of the address. A word counts as a first name if it appears at least 20 times right after a surname. Fathers’ initials, business words (shop, service) and surnames written next to first names were removed. That leaves 1,198,955 people, slightly fewer than the 1,206,134 in Numele bunicilor: those left with no first name dropped out.

On the map, a name’s share in a commune is pulled towards the county average, so small communes do not flicker. Commune maps exist only for names with at least 500 bearers (377 names); those with 50–499 bearers get a county map only.

The score: for each first name, how often it appears in Moldavia against Muntenia and Oltenia, fitted on 18 counties far from the Milcov; the 80 names with the largest difference are kept, and each person gets their average. Communes with fewer than 20 people carrying such names stay uncoloured.

The five groups: k-means on the first 6 principal components of the name profiles, with no coordinates; the most compact of 40 starts is kept. Communes in Dobruja and Bucharest are left out of the match counts, since they belonged to none of the three lands. Groups by distance: k-means with five groups on the coordinates of the same communes. The code and checks are in the project folder.