According to
Ján Steinhübel and other Slovak historians, Géza only retained the administration of the region of
Nyitra (present-day Nitra, Slovakia) and gave the eastern territories of their father's duchy, which were centered around
Bihar (present-day Biharia,
Romania), to his brother, Ladislaus. The Hungarian historian Gyula Kristó likewise says that this division of Béla's one-time duchy is "probable". The historians Gyula Kristó and Ferenc Makk write that Géza seems to have married a German countess named Sophia around this time. Géza had the right to coinage in his duchy. The silver half-denars minted for him bore the inscriptions
DUX MAGNUS ("Duke Magnus") and
PANONAI ("Kingdom of Hungary"). Géza closely cooperated with the king between 1064 and 1071. For instance,
they jointly routed an invading army which had plundered the eastern territories of the kingdom at
Kerlés (present-day Chiraleş, Romania) in 1068. The identification of the invaders is uncertain: the
Annales Posonienses writes of
Pechenegs, the
Illuminated Chronicle and other 14th- and 15th-century Hungarian chronicles refer to
Cumans, and a Russian chronicle identifies them as Cumans and
Vlachs. Modern historians have concluded that they were Pechenegs. Géza's and Solomon's relationship only began to worsen during
the siege of the
Byzantine fortress of
Belgrade in 1071. Its commander preferred to surrender to Géza instead of the king, and the Byzantine envoys who arrived in the Hungarian camp after the fall of Belgrade only negotiated with Géza. The division of the booty also gave rise to a new conflict between Solomon and Géza. Although Géza accompanied the king on
a new campaign against the
Byzantine Empire in 1072, his brother Ladislaus stayed behind with half of the troops of their duchy. The conflict between the king and his cousins was sharpened by Solomon's main advisor,
Count Vid, who wanted to acquire the dukes' domains for himself. However, Solomon and Géza, who were convinced that they needed foreign reinforcements before attacking the other party, concluded a truce which was to last from 11 November 1073 to 24 April 1074. Géza sent his brothers to Poland and
Rus' to seek assistance against Solomon. At a meeting in the
Szekszárd Abbey, Count Vid persuaded the king to break the truce in order to unexpectedly attack Géza who was "hunting in Igfan Forest" to the east of the river
Tisza. Although the abbot of the monastery, which had been established by Géza's father, warned the duke of the king's plans, the royal army crossed the river and routed Géza's troops in the
battle of Kemej on 26 February 1074. : a descending angel places a crown on the head of Prince Géza. (
Chronicon Pictum, 1358) A legend preserved in the
Illuminated Chronicle mentions that before the battle, Ladislaus "saw in broad daylight a
vision from heaven" of an angel placing a crown on Géza's head. Another legendary episode also predicted the dukes' triumph over the king: an "
ermine of purest white" jumped from a thorny bush to Ladislaus's lance and then onto his chest. in 1074, the warriors of Prince Géza led by Prince
Ladislaus on a white horse (
Chronicon Pictum, 1358) From the battlefield, Géza and his retinue hastened towards
Vác where he came upon his brother Ladislaus and their brother-in-law, Duke
Otto I of Olomouc. The latter, accompanied by
Czech reinforcements, arrived in Hungary in order to assist Géza against Solomon. In the ensuing battle,
fought at Mogyoród on 14 March 1074, Géza "with the troops from Nitria was stationed in the centre", according to the
Illuminated Chronicle. During the battle, Géza and Ladislaus changed their standards in order to bewilder Solomon who was planning to attack Géza. Géza and his allies won a decisive victory and forced the king to flee from the battlefield and to withdraw to Moson at the western frontier of Hungary. Géza "made"
Kapuvár,
Babót,
Székesfehérvár and "other castles secure with garrisons of the bravest soldiers", thus taking possession of almost the entire kingdom. ==His reign (1074–1077)==