Byzantine Bithynia

1302 Ottoman-Byzantine military engagement

1329 battle

1328–1331 capture of the Byzantine city of Nicaea

Late Roman (562) bridge in Serdivan, Sakarya, Turkey

The Opsician Theme (, thema Opsikiou) or simply Opsikion (Greek: , from ) was a Byzantine theme (a military-civilian province) located in northwestern Asia Minor (modern Turkey). Created from the imperial retinue army, the Opsikion was the largest and most prestigious of the early themes, being located closest to Constantinople. Involved in several revolts in the 8th century, it was split in three after , and lost its former pre-eminence. It survived as a middle-tier theme until after the Fourth Crusade.

1096 battle in the People's (First) Crusade

The Optimatoi (, from , "the Best Men") were initially formed as an elite Byzantine military unit. In the mid-8th century, however, they were downgraded to a supply and logistics corps and assigned a province (thema) in north-western Asia Minor, which was named after them. As an administrative unit, the 'Theme of the Optimatoi''' (, thema Optimatōn'') survived until the Ottoman conquest in the first decades of the 14th century.

Unsuccessful attempt by the Umayyad Caliphate to capture the Byzantine city of Nicaea in 727

Byzantine saint

mosque and former Byzantine church

Byzantine rebel leader active in Bithynia

ruined Early Christian basilica semi-submerged in Lake İznik, Türkiye

thumb|Bithynia marked in radium green Gordoservon or Gordoserbon or Gordoserba (; ) was an early medieval Byzantine city, and a bishopric, suffragan of the Metropolis of Nicaea, in the region of Bithynia, Asia Minor. It is mentioned in several ecclesiastical sources from the period between the 7th and the 9th century. Most notably, the city is mentioned in the acts of the Council of Trullo (691-692), as a seat of bishop Isidore, who attended the council.

Xerigordos (), often incorrectly Xerigordon in modern historiography, was a castle in Anatolia (today Turkey) that served as the setting of the Siege of Xerigordos as a part of the People's Crusade in 1096. The contemporary records assert that the fortress was located on a hill and its water supply came from both a water well and a spring just outside the walls. The exact location has not yet been identified. Albert of Aix wrote that it was about three miles away from Nicaea.

1211 battle of the Nicaean-Latin Wars

ruined Byzantine-era monastery in Turkey

battle between two rival Byzantine armies in 1057

Greek Orthodox monastery near Tirilye, Turkey

monastery in Turkey

Byzantine monk