Nicaea in the context of Anatolian Seljuks

The Sultanate of Rum, or Seljuk Empire of Rum, was a culturally Turco-Persian Sunni Muslim state, established over conquered Byzantine territories and peoples (Rum) of Anatolia by the Seljuk Turks following their entry into Anatolia after the Battle of Manzikert in 1071. The name Rum was a synonym for the medieval Eastern Roman Empire and its peoples, as it remains in modern Turkish. The name is derived from the Aramaic (romī) and Parthian (frwm) names for ancient Rome, via the Greek Ῥωμαῖοι (Romaioi) meaning Anatolia. It is considered to be the beginning of Turkish history in Anatolia.

The Sultanate of Rum seceded from the Seljuk Empire under Suleiman ibn Qutalmish in 1077. It had its capital first at Nicaea and then at Iconium. It reached the height of its power during the late 12th and early 13th century, when it succeeded in taking key Byzantine ports on the Mediterranean and Black Sea coasts. In the east, the sultanate reached Lake Van. Trade through Anatolia from Iran and Central Asia was developed by a system of caravanserai. Especially strong trade ties with the Genoese formed during this period. The increased wealth allowed the sultanate to absorb other Turkish states that had been established following the conquest of Byzantine Anatolia: Danishmendids, House of Mengüjek, Saltukids, Artuqids.

Hipparchus (/hɪˈpɑːrkəs/; Greek: Ἵππαρχος, Hípparkhos; c. 190 – c. 120 BC) was a Greek astronomer, geographer, and mathematician. He is considered the founder of trigonometry, but is most famous for his incidental discovery of the precession of the equinoxes. Hipparchus was born in Nicaea, Bithynia, and probably died on the island of Rhodes, Greece. He is known to have been a working astronomer between 162 and 127 BC.

Hipparchus is considered the greatest ancient astronomical observer and, by some, the greatest overall astronomer of antiquity. He was the first whose quantitative and accurate models for the motion of the Sun and Moon survive. For this he certainly made use of the observations and perhaps the mathematical techniques accumulated over centuries by the Babylonians and by Meton of Athens (fifth century BC), Timocharis, Aristyllus, Aristarchus of Samos, and Eratosthenes, among others.

The First Council of Nicaea (/naɪˈsiːə/ ny-SEE-ə; Ancient Greek: Σύνοδος τῆς Νικαίας, romanized: Sýnodos tês Nikaías) was a council of Christian bishops convened in the Bithynian city of Nicaea (now İznik, Turkey) by the Roman Emperor Constantine I. The Council of Nicaea met from May until the end of July 325.

This ecumenical council was the first of many efforts to attain consensus in the church through an assembly representing all Christendom. Hosius of Corduba may have presided over its deliberations. Attended by at least 200 bishops, its main accomplishments were the settlement of the Christological issue of the divine nature of God the Son and his relationship to God the Father, the construction of the first part of the Nicene Creed, the mandating of uniform observance of the date of Easter, and the promulgation of early canon law.

The Second Council of Nicaea is recognized as the last of the first seven ecumenical councils by the Eastern Orthodox Church and the Catholic Church. In addition, it is also recognized as such by Old Catholics and others. Protestant opinions on it are varied.

The Council assembled in 787 AD in Nicaea (site of the First Council of Nicaea; present-day İznik, Bursa, in Turkey), to restore the use and veneration of icons (or holy images), which had been suppressed by imperial edict inside the Byzantine Empire during the reign of Leo III (717–741). His son, Constantine V (741–775), had held the Council of Hieria to make the suppression official.

İznik (Turkish pronunciation: [izˈnik]) is a municipality and district of Bursa Province, Turkey. Its area is 753 km, and its population 44,236 (2022). The town is at the site of the ancient city of Nicaea, from which the modern name derives. The town lies in a fertile basin at the eastern end of Lake İznik, with ranges of hills to the north and south. As the crow flies, the town is only 90 kilometres (56 miles) southeast of Istanbul but by road it is 200 km (124 miles) around the Gulf of İzmit. It is 80 km (50 miles) by road from Bursa.

İznik has been a district centre of the province of Bursa since 1930 but belonged to the district of Kocaeli between 1923 and 1927. It was a township of Yenişehir district (connected to Bilecik before 1926) between 1927 and 1930.

Lake İznik (Turkish: İznik Gölü) is a freshwater lake in the Province of Bursa, Turkey. It is around 32 km (20 mi) in length and 10 km (6+1⁄5 mi) in width with a maximum depth of about 80 m (260 ft; 44 fathoms). The town of Iznik (historically known as Nicaea) lies at its eastern end. The lake's Ancient Greek name was Askania (Ἀσκανία); the Latin name was Ascania.

Christianity in Asia has its roots in the very inception of Christianity, which originated from the life and teachings of Jesus in 1st-century Roman Judea. Christianity then spread through the missionary work of his apostles, first in the Levant and taking roots in the major cities such as Jerusalem and Antioch. According to tradition, further eastward expansion occurred via the preaching of Thomas the Apostle, who established Christianity in the Parthian Empire (Iran) and India. The very First Ecumenical Council was held in the city of Nicaea in Asia Minor (325). The first nations to adopt Christianity as a state religion were Armenia in 301 and Georgia in 327. By the 4th century, Christianity became the dominant religion in all Asian provinces of the Eastern Roman Empire.

After the First Council of Ephesus in 431 and the Nestorian Schism, the Nestorian Christianity developed. Nestorians began converting Mongols around the 7th century, and Nestorian Christianity was probably introduced into China during the Tang dynasty (618–907). Mongols tended to be tolerant of multiple religions, with several Mongol tribes being primarily Christian, and under the leadership of Genghis Khan's grandson, the great khan Möngke, Christianity was a small religious influence of the Mongol Empire in the 13th century.