From 1323/1324 until 1362, Orhan Ghazi was the second bey of the Ottoman Beylik. As Osman's son, he was born in Söğüt. Orhan concentrated his efforts in the early stages of his rule on capturing the majority of northern Anatolia. The bulk of these lands were under Byzantine authority, and he defeated Byzantine Emperor Andronikos III Palaiologos in his first fight at Pelekanon. The Ahis of Ankara and Karasids of Balıkesir were also conquered by Orhan. Orhan benefitted enormously from a succession of civil conflicts following the nine-year-old Byzantine emperor John V Palaiologos. The substitute John VI Kantakouzenos married his daughter Theodora to Orhan. They deployed Ottoman troops against the competing armies of the empress dowager, allowing them to plunder Thrace during the Byzantine civil war of 1341 to 1347. Kantakouzenos employed Ottoman soldiers against John V in the Byzantine civil war of 1352 to 1357, allowing them to use a European castle at impe about 1352. Two years later, a massive earthquake struck Gallipoli (modern Gelibolu), and Orhan's son, Süleyman Pasha, seized the town, providing the Ottomans with a powerful bridgehead into mainland Europe. Orhan was "the greatest of the Turkmen monarchs and the wealthiest in fortune, territories, and military forces," according to Muslim writer Ibn Battuta.
Osman Gazi died in the year 1323 or 1324, and Orhan became his successor. When Orhan succeeded his father, he offered to his brother, Alaeddin, to divide the newly formed Empire according to Ottoman tradition. The latter disagreed, claiming that their father had named Orhan the only heir and that the Empire should not be split. He only agreed to take a portion of the profits from a small hamlet near Bursa. "Since thou, my brother, will not take the sheep and herds that I give thee, be the shepherd of my people; be my Vizier," Orhan said. The name vizier, or vezir in Ottoman, came from the Arabic word wazīr, signified load carrier. According to eastern historians, Alaeddin accepted his brother's weight of authority by accepting the post. Alaeddin, like many of his predecessors in that position, did not typically command the troops in person, preferring instead to focus on the establishment and control of the state's civil and military institutions.
According to some sources, the Ottomans stopped acting like vassals to the Seljuk monarch during Alaeddin's reign. For example, they stopped stamping money with his picture on his instruction or using his name in public prayers. Others credit Osman with these improvements, but the great majority of Asian authors credit Alaeddin with the establishment of rules governing the attire of the Empire's numerous subjects, as well as the construction and funding of a standing force of regular troops. In addition, the celebrated corps of Janissaries was founded on his advice and that of a contemporary Turkish statesman, an institution that European writers erroneously fix at a later date and ascribe to Murad I.
Alaeddin, by his military legislation, may indeed be said to have organized victory for the Ottoman dynasty. An entire century before Charles VII of France formed his fifteen permanent men-at-arms, which are often considered the first modern standing army, he organized a standing army of regularly paid and trained soldiers and horses for the Ottoman Beylik. Ertuğrul and Osman I, Orhan's forefathers, had fought at the head of armed vassals and volunteers. When summoned for each expedition, this army marched to their prince's flag on horseback and dissolved as soon as the campaign was ended. Alaeddin was adamant about ensuring future success by creating a paid infantry corps that would be maintained on standby at all times. Yaya, or piyade, were the names given to these forces. With their leaders, they were split into tens, hundreds, and thousands. Their salary was excellent, and their arrogance quickly raised concern among their rulers. Orhan wanted to give them a check, so he sought advice from his brother Alaeddin and Kara Khalil andarl (of House of Candar), who was related to the royal family through marriage. Andarl presented a proposition to his master and the vizier. The infamous Janissaries were born of this, and for a long time, were considered the scourge of the Balkans and Central Europe until Sultan Mahmud II disbanded them in 1826. Çandarlı offered to Orhan that he forms an army exclusively made up of conquered places' children.
He further believed that the establishment of Janissary from captured children would encourage others to adopt, not only from conquered children but from a multitude of their friends and relatives who would volunteer to join the Ottoman lines. Following this suggestion, Orhan chose a thousand of the best lads from Christian households who had been defeated. According to their skills, recruits were taught for specific jobs and assigned to positions ranging from professional soldiers to Grand Vizier. This tradition persisted for centuries until Sultan Mehmet IV's rule.
Orhan began a series of conquests of Byzantine areas in northwest Anatolia with the aid of Ghazi commanders at the head of his light cavalry armies. Mudanya was first seized in 1321 in the Sea of Marmara, at the city of Bursa. He then dispatched a column under Konur Alp to conquer the West Black Sea coast, another under Aqueda to capture Kocaeli, and a third to capture the Sea of Marmara's southeast shore. Then he used diplomatic talks to take the city of Bursa. Evrenos Bey, the Byzantine commander of the Bursa fort, became the leader of a light cavalry unit. His sons and grandchildren served Ottoman Beylik to capture and retain numerous territories throughout the Balkans. After taking Bursa, Orhan sent cavalry soldiers along the Bosphorus, seizing Byzantine coastal cities in Marmara. Along the Bosphorus shore, there were also sightings of Ottoman light cavalry. On the peninsular regions of Kocaeli, the Byzantine Emperor Andronicus III assembled a mercenary army and headed out towards Anatolia.
Nevertheless, he encountered Orhan's forces in the present-day cities of Darica, at a place named Pelekanon at the time, not far from Üsküdar. Orhan's disciplined men routed the Byzantine army in the subsequent battle of Pelekanon. Andronicus thus abandoned his plan to reclaim the Kocaeli territories and never again fought an Ottoman army on the battlefield. After a three-year siege that ended in 1331, Nicaea (second only to Constantinople in the Byzantine Empire) surrendered. In 1337, the city of Nicomedia (now Izmit) was also taken. Orhan delegated leadership to his eldest son, Suleyman Pasha, who had overseen the siege efforts. By conquering Scutari (now Üsküdar) in 1338, the Ottomans took control of Northwest Anatolia. The Byzantines still controlled the shore strip from Sile on the Black Sea to Scutari and the city of Amastris (now Amasra) in Paphlagonia. Still, they were so dispersed and isolated that the Ottomans did not see them as a danger. Then, in 1345, there was a shift in approach. Orhan seized a Turkish principality, Karesi (present-day Balıkesir and environs), instead of winning land from non-Muslims. According to Islamic military theory, the territories under Islamic authority were abodes of peace, while the rest of the world was to be abodes of conflict. Conducting a war was considered a positive action in places where fighting was practised.
In the instance of Karesi, the monarch had died, leaving two sons with equal claims to the position of Emir. For this reason, there was a brawl between the two claimant princes' armed followers. Orhan pretended to be a peacemaker to justify his invasion. The two brothers were forced to the fortress of Pergamum, their capital city, at the end of the Ottoman assault (now Bergama). One of them was murdered, while the other was apprehended. Orhan's holdings were expanded to include the areas around Pergamum and Palaeocastro (Balıkesir). This conquest was especially significant since it brought Orhan's lands to Çanakkale, on the Anatolian side of the Dardanelles Straits. With the win of Karesi, the Ottoman Beylik absorbed virtually all of northern Anatolia, and the four cities of Bursa, Nicomedia İzmit, Nicaea, İznik, and Pergamum (Bergama) became strongholds of its authority. Orhan's Ottoman Principality had four provinces at this point in his conquests:
Following the conquest of Karesi, there was a twenty-year era of calm. During this period, the Ottoman sultan was busy refining the civil and military institutions that his brother had established and maintaining internal order, creating and endowing mosques and schools, and erecting massive public structures, many of which still exist today. Except for capturing Ankara from the commercial-religious guild of Ahis, Orhan did not pursue any further conquests in Anatolia. Before Osman's time, the Mongol invasion of Central Asia, Iran, and later East Anatolia was a significant factor in the spread of Turkish inhabitants across Anatolia. Following the defeat of the Ilkhanate Mongols by the Anatolian Sultanate of Rum, Turkish peoples established several principalities. Even though they were all of Turkish descent, they were all competitors for dominance in Anatolia. Orhan had cordial ties with Andronicus III Palaeologus after the Byzantine loss at the Battle of Pelekanon and maintained them with several of his successors. As a result, the Ottoman Empire enjoyed twenty years of relative peace. However, when the Byzantine civil war of 1341–1347 depleted the Empire's final resources, the Emirs of Turkish kingdoms' auxiliary troops were regularly summoned and deployed in Europe. Orhan was recognized as the most powerful king of the Turks by Emperor John VI Cantacuzene in 1346. He wanted to firmly bind the Ottoman armies to his interests by marrying his second daughter, Theodora, to their monarch, even though they were of different creeds and were of different ages. However, dynastic weddings were typical in Byzantine and Western European history, and other cases are even more bizarre. Byzantine sources go into great detail on the splendour of Orhan and Theodora's wedding at Selymbria (Silivri). Orhan and Theodora have visited his imperial father-in-law at Üsküdar (formerly Chrysopolis), a suburb of Constantinople on the Asiatic side of the Bosporus, where there was a festive display. However, when Byzantines were attacked by roving migrant Turcoman gangs who had crossed the Marmara Sea and Dardanelles and pillaged numerous cities in Thrace, the relationship became strained. The Byzantines had to employ greater forces to cope with these raids after a succession of them.
Descent of Byzantine Empire
The Byzantine Empire collapsed under Orhan's tenure as Ottoman emir, partially due to the aspirations of Italian maritime powers and the invasion of the Turcomans and another city Turks, but also due to internal civil conflicts. During these years, the Byzantine Empire weakened to the point that commercial dominance in the surrounding waters became a point of the war for the Italian maritime city-states. Galata, a distinct Genoese city across the Golden Horn from Constantinople, belonged to the Republic of Genoa. The Genoese had previously battled the Byzantines in 1348 when the Byzantines reduced their customs taxes to lure commerce to the Byzantine side of the Golden Horn. The struggle for business between Genoa and Venice resulted in a war in 1352. In an attempt to prevent a Venetian fleet from destroying their ships in Golden Horn, the Genoese assaulted Constantinople's sea defences, forcing the Byzantines to unite with the Venetians. The Venetians gathered a substantial naval force, including leased ships from Peter IV of Aragon and John VI Cantacuzene's Byzantine Empire. The Venetians and their Byzantine allies were defeated in a naval battle between the Venetian fleet under Niccolo Pisani and the Genoese fleet under Paganino Doria. Orhan was at odds with the Venetians, whose ships and piratical incursions were causing havoc in his seaward territories and who had dismissed his diplomatic overtures. Because the Venetians were John VI's friends, Orhan dispatched an auxiliary army over the straits to Galata, where it collaborated with the Genoese. He also began settling migratory Turcomans and town-dwelling Turks in Gelibolu (Gallipoli), a key city and fortress destroyed by a devastating earthquake and had been evacuated by its people. Suleyman turned down several cash offers from John VI to empty the castle and city. The Emperor appealed with his son-in-law Orhan to meet and address the problem in person, but the request was either denied or could not be fulfilled owing to Orhan's age and ill-health. Because of the outbreak of hostilities between John VI and his co-emperor and son-in-law John V Palaeologus, this military situation remained unsolved. Cantacuzene's son Matthew was crowned co-emperor when John V was removed from his imperial office and banished to Tenedos. However, with Venetian assistance, John V returned from exile and staged a coup, seizing control of Constantinople. Even though the two men agreed to share authority, John VI resigned as Emperor and became a monk. Orhan backed whatever side would benefit the Ottomans, and each of these two powerful rivals was constantly enlisting Orhan's help against the other.
Orhan was one of the future Ottoman Sultans who lived the longest and reigned the longest. He had put most of the state's authority in the hands of his second son Murad in his final years, and he lived a reclusive life in Bursa. Khalil, Orhan and Theodora's son, was kidnapped in the Bay of Izmit in 1356. A Genoese commercial boat captain was able to seize the young prince and transport him to Phocaea on the Aegean Sea, under Genoese authority. Orhan was enraged by the kidnapping and had negotiations with his brother-in-law, John V Palaeologus, the sole Byzantine Emperor at the time. According to the agreement, John V sent a Byzantine naval fleet to Phocaea, paid the 100,000 hyperpyrexia ransom requested, and returned Khalil to Ottoman territory. Suleyman Pasha, Orhan's eldest and most experienced son and potential heir, died in 1357 after falling off a horse at Bolayir on the coast of the Sea of Marmara. Suleyman's horse was also buried with him, and their graves can still be seen today. Orhan was believed to have been deeply impacted by his son's death. Orhan died shortly after, most likely as a result of natural causes. However, it appears that his health was strained as a result of his son's death. Orhan died at Bursa in 1362, at the age of eighty, following a thirty-six-year reign. At Bursa, he is buried with his wife and children in the Gümüşlü Kumbet türbe (tomb).
Orhan and Stefan Uroš IV Dušan were considering a possible alliance in 1351. There was a plan to marry Orhan or one of his sons to Dušan's daughter Theodora. However, Serbian diplomats were attacked by Nikephoros Orsini, leading to a breakdown in talks, the annulment of the marriage, and the resumption of hostilities between Serbia and the Ottoman state.
Orhan Gazi was played in the Turkish television series Kuruluş "Osmancık" (1988).