Gulf of İzmit in the context of "İznik"

İzmit (Turkish pronunciation: [ˈizmit]) is a municipality and the capital district of Kocaeli Province, Turkey. Its area is 480 km, and its population is 376,056 (2022). The capital of Kocaeli Province, it is located at the Gulf of İzmit in the Sea of Marmara, about 100 km (62 mi) east of Istanbul, on the northwestern part of Anatolia. Kocaeli Province (including rural areas) had a population of 2,079,072 inhabitants in 2022, of whom approximately 1.2 million lived in the largely urban İzmit City metro area made up of Kartepe, Başiskele, Körfez, Gölcük, Derince and Sapanca (in Sakarya Province). Similar to Istanbul, the area of İzmit is coterminous with its province. It is also the most populated of any city or town in Turkey whose name isn't shared with the province it is located in.

İzmit was known as Nicomedia and Ólbia in antiquity, and was the eastern and most senior capital city of the Roman Empire between 286 and 324, during the Tetrarchy introduced by Diocletian. Following Constantine the Great's victory over co-emperor Licinius at the Battle of Chrysopolis in 324, Nicomedia served as an interim capital city for Constantine between 324 and 330. During the Ottoman Empire, İzmit was the capital of the Sanjak of Kocaeli. In the present day, Istanbul-İzmit area is one of the main industrial regions in Turkey.

Kocaeli Province (Turkish: Kocaeli ili, pronounced [koˈdʒaeli]) is a province and metropolitan municipality of Turkey and one of only three not to have the same official name as its capital, İzmit, which is thus also sometimes called Kocaeli. Its area is 3,397 km (1,312 sq mi), and its population is 2,102,907 (2023). The province is the successor of the Ottoman-era Sanjak of Kocaeli. The largest towns in the province are İzmit and Gebze. The traffic code is 41.

The province is located at the easternmost end of the Sea of Marmara around the Gulf of İzmit. Kocaeli is bordered by the province of Istanbul and the Marmara Sea to the west, the Black Sea to the north, the province of Sakarya to the east, the province of Bursa to the south and the province of Yalova to the southwest. The metropolitan area of Istanbul extends to the Kocaeli-Istanbul provincial border.

Karamürsel is a municipality and district of Kocaeli Province, Turkey. Its area is 262 km, and its population is 59,676 (2022). It is on the south coast of the Gulf of İzmit. Before its conquest by the Ottomans it used to be called by the Greek name of Praenetos (Πραινετός in Greek). The modern name commemorates Kara Mürsel who founded the Ottoman navy and designed distinctive galley ships, called kadırgas, for it.

Karamürsel holds special significance for the Turkish Navy, as it was here in 1323 that the Ottoman Empire first established an outlet to the sea, thus laying the foundations for the Ottoman Navy which would go on to dominate the eastern Mediterranean for several centuries.

Otoyol 5 (English: Motorway 5), named the Kocaeli Gebze-Bursa-İzmir Motorway (Turkish: Kocaeli Gebze-Bursa-İzmir Otoyolu) and abbreviated as O-5, is a toll motorway in Turkey. Since being completed in 2019, it connects the Istanbul and Kocaeli metropolitan areas with İzmir, via Bursa and Balıkesir. The O-5 runs parallel to the D575 and the D565 for most of its length and is a major motorway in Turkey as it provides a direct connection between Kocaeli and its surrounding metropolis to the country's 3rd largest (İzmir) and 4th largest (Bursa) cities, bypassing the Gulf of İzmit via the Osman Gazi Bridge. The O-5 also makes up part of the International E-road network E881 thus making it one of the most extensive and expensive transport megaprojects.

The western part of the Bursa Beltway, which is part of the O-5, was completed during the 2000s. The rest of the O-5 has been under construction since the early 2010s, with the first portion opened from Altinova to Gemlik in April 2016. As of April 2017, the O-5 is open in two separate sections: the 105.5 km (65.6 mi) section from its northern terminus in Kocaeli, Gebze to Bursa, across the Osman Gazi Bridge along with a 18.2 km (11.3 mi) section from Kemalpaşa to its southern terminus in İzmir. The final section, Karacabey to Akhisar, opened on August 5, 2019.

40°43′24″N 29°30′08″E / 40.72339°N 29.50224°E / 40.72339; 29.50224Helenopolis (Greek: Ἑλενόπολις) or Drepana (Δρέπανα) or Drepanon (Δρέπανον) was an ancient Thracian and later Greco-Roman and Byzantine town in Bithynia, Asia Minor, on the southern side of the Gulf of Astacus. Helenopolis has been identified with the modern village of Hersek, in the district of Altınova, Yalova Province. It is traditionally considered as the birthplace of Saint Helena.

Gölcük, historically known as Diolkides, is a municipality and district of Kocaeli Province, Turkey. Its area is 217 km, and its population is 175,940 (2022). Gölcük is located on the southern shore of the Gulf of İzmit, which is the easternmost inlet of the Sea of Marmara.

Gölcük is home to the Gölcük Naval Base and Gölcük Naval Shipyard of the Turkish Navy. A Ford Otosan automobile plant is also located in the district.

The Osman Gazi Bridge (Turkish: Osmangazi Köprüsü) is a suspension bridge spanning the Gulf of İzmit at its narrowest point, 2,620 m (8,600 ft). The bridge links the Turkish city of Gebze to the Yalova Province and carries the O-5 motorway across the gulf.

The bridge was opened on 1 July 2016 to become the then-longest suspension bridge in Turkey and the fourth-longest (ninth-longest as of 2025) suspension bridge in the world by the length of its central span.