Any Romanian will tell you that they are direct descendents of the Dacians who were Romanised and have continued living in the lands of Romania. This justifies the incorporation of Transylvania, with its majority Romanian population, to Romania after WW1. However, the Hungarians continue to argue against this theory. Visits to regional Romanian history museums all give the same view of a continuity from Dacia to the present day avoiding anything dubious. Hungarian history books, although condemning the Romanian's single minded attempts to justify the continuity theory, fall into the trap of being a equally single minded in arguing against the Romanians!
There are no written documents from around the time of the Hungarian conquest concerning the area of modern Transylvania apart from the the "Gesta Hungarorum". It is thought that this was written by Peter, a high priest in Buda, during the time of King Bela III in the late 12th century. This is some 300 years after the Maygar tribes entered the Carpathian basin, some 200 years after the first Hungarian expansion into Transylvania, and around when the Szekely and Saxon peoples were moved into the new Transylvanian lands.
The "Gesta Hungarorum" contains correct facts, inaccurate facts, and information on Transylvania that cannot be confirmed from other sources. Some of the work is directly from earlier sources, and covers the history of the Magyar peoples moving into the Carpathian basin. The following are some commonly referenced parts with commentary regarding Transylvania. You may choose to believe them or not!
Regarding the area of Bihor:
Gesta hungarorum says:
....The lands between the Tisa and the forest towards Transylvania and from the Mures river to the Somes river was occupied by Duke Morout, whose grandson was called Men-Marot by the Hungarians. The lands were inhabited by people called Khozar. The Hungarian leader Arpad, sends messengers to Bihar and asks Menumorout to cede the territory between the Somes river and Mezes mountains. Menumorout refuses, referring to his lord the Byzantium Emperor. After three days of siege at Sotmar (now Szatmar = Satu Mare) the castle is taken. The story is told once again, but this time Menumorurt who had earlier declined "with a Bulgarian heart" now gives the lands and his daughter.....
Some Hungarians propose that the names Morout and Menumorout were invented from from earlier chronicles regarding Morot, the leader the Hungarians met in Pannonia, other suggest these names could have come from the Hungarian name for Moravians whom they defeated in 906.
The Magyars tribes were joined by some other tribes when they moved into the Carpathian basin. One of these tribes was related to the Khazar. It is know that a tribe which originally settled in the Bihor region was later known as the Szekely and were moved to the south east of Transylvania.
Much of the Balkans was under Bulgarian rule but had fallen to Byzantium before the Magyar tribes entered. Any Dukes met by the Hungarians were likely to be "Bulgarian", and the population might be expected to be a mix of Slavs and Romanised peoples, as found in other Bulgarians territories. Other sources record the presence of Avars (kingdom existed until 796), Slavs, Moravians (Slavic state until defeated by Hungarians in 906), Bulgarians (Empire extended to this area in 9th century) and Gepids (Germanic kingdom existing until 567). Gesta hungarorum and Russian Primay Chronicle also includes Vlachs.
Regarding the area of Banat:
Gesta hungarorum says:
....The lands between the Mures river and the castle of Orsova was occupied by Duke Glad, who came from the castle of Vidin. His descendent was Ahtum, who later in the time of King Stephen was killed by Csanad, the son of Bobuka. The Hungarians sent an army against Duke Glad and subdued the population between the Mures and Temes rivers. When they tried to pass the Temes river Glad came against them with a great army including Cuman, Bulgarian and Vlach support. On the following day the Hungarians defeated the enemy......
It is known that the Bulgarians fought the newly arrived Hungarians, and Bulgarian armies may have included Vlachs. Several centuries later Bulgaria was to create a second empire of Slavs and Vlachs south of the Danube. Ahtum is a known historical Prince who lived in the region of Banat and was subdued by King Stephen at the start of the 11th century.
Regarding the area of Transylvania:
Gesta hungarorum says:
....Teteny, the father of Horka, found out from the inhabitants about the territory beyond the forest, where some Vlach Gelu ruled.....and the territory beyond the forrest was held by the decedents of Teteny until the time of Stephen, and would have continued to be if Gyula and his sons Bolya and Bonyha had been willing to adopt Christianity and not act against the king. Teteny sent a spy beyond the forrest and he reported that it was rich in salt, gold and many good rivers. The inhabitants of that country were the most unworthy in the world because they were Vlachs and Slavs. A fierce battle started, in which the soldiers of Gelu were defeated. ... Gelu was pursued by warriors of Teteny and killed. When the inhabitants of the country saw the death of their lord, they wanted to make peace and chose Teteny as their leader......
The Hungarian chief Gyula is a known historic character and was subdued by King Stephen in 1002. Hungarians ruled the lands of Transylvania by maintaining a typically Slavic system of Voivode and local Knez rulers suggesting that the pre-Hungarian organisation was maintained. This system re-emerged a couple of centuries later when the Vlachs founded the countries of Moldavia and Wallachia. These may support the view of continuity from a previous Slavic ruled period.