A series of civil wars surrounding the ascension of the nine-year-old Byzantine emperor John V Palaiologos greatly benefited Orhan.

[citation needed] In the Byzantine civil war of 1341–1347, the regent John VI Kantakouzenos married his daughter Theodora to Orhan and employed Ottoman warriors against the rival forces of the empress dowager, allowing them to loot Thrace.

[2][3] A major earthquake devastated Gallipoli (modern Gelibolu) two years later, after which Orhan's son, Süleyman Pasha, occupied the town, giving the Ottomans a strong bridgehead into mainland Europe.

According to Muslim scholar Ibn Battuta, Orhan was "the greatest of the Turcoman kings and the richest in wealth, lands, and military forces".

According to some authorities, it was in Alaeddin's time, and by his advice, that the Ottomans ceased acting like vassals to the Seljuk ruler: they no longer stamped money with his image or used his name in public prayers.

It was by his advice and that of a contemporary Turkish statesman that the celebrated corps of Janissaries was formed, an institution which European writers erroneously [citation needed] fix at a later date, and ascribe to Murad I.

Out of this arose the renowned corps of Janissaries, which was considered the scourge of the Balkans and Central Europe for a long time, until it was abolished by Sultan Mahmud II in 1826.

[citation needed]He also claimed that incorporating children of the conquered would induce other people to enlist: their friends and relations, who would come as volunteers to join the Ottoman ranks.

The Byzantines still controlled the coastal strip from Şile on the Black Sea to Scutari and the city of Amastris (now Amasra) in Paphlagonia, but these were so scattered and isolated as to be no threat to the Ottomans.

With the conquest of Karesi, nearly the whole of northwestern Anatolia was included in the Ottoman Beylik, and the four cities of Bursa, Nicomedia, Nicaea, and Pergamum had become strongholds of its power.

During this time, the Ottoman sovereign was actively occupied in perfecting the civil and military institutions which his brother had introduced, in securing internal order, in founding and endowing mosques and schools, and in the construction of vast public edifices, many of which still stand.

Turkish peoples had founded a number of principalities after the demise of the Anatolian Sultanate of Rum, after its defeat by the Ilkhanate Mongols.

After the Byzantine defeat of the Battle of Pelekanon, Orhan developed friendly relations with Andronicus III Palaeologus, and maintained them with some of his successors.

He aspired to attach the Ottoman forces permanently to his interests, and hoped to achieve this by giving his second daughter, Theodora, in marriage to their ruler, despite differences of creed and the disparity of age.

In the following year, Orhan and Theodora visited his imperial father-in-law at Üsküdar, (then Chrysopolis) the suburb of Constantinople on the Asiatic side of the Bosporus where there was a display of festive splendor.

However, this close relationship soured when Byzantines suffered from marauding migrant Turcoman bands that had crossed the Marmara Sea and Dardanelles and pillaged several towns in Thrace.

Ibn Battuta gave the following account of Orhan during his reign: The greatest of the kings of the Turcomans and the richest in wealth, lands and military forces.

The Venetians assembled a large naval force, including hired fleets from Peter IV of Aragon and from the Byzantine Empire of John VI Cantacuzene.

[13] Orhan opposed the Venetians, whose fleets and piratical raids were disrupting his seaward provinces, and who had met his diplomatic overtures with contempt.

In the midst of the distress and confusion that the Byzantine Empire now suffered, Orhan's eldest son, Suleyman Pasha, captured the Castle of Tzympe (Cinbi) in a bold move which gave the Turks a permanent foothold on the European side of the Dardanelles Straits.

He also started to settle migrant Turcomans and town-dwelling Turks in the strategic city and castle of Gelibolu (Gallipoli), which had been devastated by a severe earthquake and was therefore evacuated by its inhabitants.

As to the agreement, John V with a Byzantine naval fleet went to Phocaea, paid the ransom demanded of 100,000 hyperpyra, and brought Halil back to Ottoman territory.

In 1357 Orhan's eldest and most experienced son and likely heir, Suleyman Pasha, died after injuries sustained from a fall from a horse near Bolayir on the coast of the sea of Marmara.