|• Mayor||İbrahim Ziyrek (AKP)|
|• Kaymakam||Eyüp Tepe|
|• District||1,394.09 km2 (538.26 sq mi)|
|• District density||23/km2 (61/sq mi)|
Oltu (Georgian: ოლთისი, Oltisi; Armenian: Ողթիկ, Voght'ik; Russian: Ольта, Olta,) is a town and district of Erzurum Province in the Eastern Anatolia region of Turkey. The mayor is İbrahim Ziyrek (AKP). The population was 19,969 in 2010.
An inscription found in Oltu’s castle has been dated to the 7th century A.D.(see below), but the settlement is known to have been established much earlier. The city-fortress had once belonged to the Mamikonian nakharars and later passed into the hands of the Bagratunis. Administratively, it was found within the borders of the region of Vok'aghe in the province of Tao. The first mention of Oltu as a fortified settlement is in the 9th century when the Georgian Bagratids occupied this region. After the death of the Iberian Kuropalates David in 1000, the troops of Emperor Basil II occupied the castles and towns in the region of Tao-Tayk‛, which included Oltu. In the following centuries, Oltu successively passed into the control of the Seljuk Turks, the Mongols and Turkmen tribes, all the while retaining its Armenian identity. The Ottomans conquered Olti from the Georgians in the sixteenth century.
In the summer of 1829, the Russians took control of the region but relinquished it to the Ottomans. During the Russo-Turkish War of 1877–78, the town was incorporated into the Russian Empire and made a part of Kars Oblast. Prior to the out break of the First World War Olti had a population of 2,373. In last months of 1918, Olti was nominally part of Democratic Republic of Georgia but it was ruled by Turkish warlords. In 1919, Oltu was annexed by the Democratic Republic of Armenia. The following year, the Turkish armies in Eastern Anatolia led by Kazım Karabekir invaded Armenia during the Turkish War of National Liberation and recovered Oltu, a territorial gain which was confirmed in subsequent treaties signed between the Turks and the Soviets.
The primary historical sight in Oltu is the castle. This impressive site covers the top of a rocky outcrop. Its walls are fortified by large round towers and salients, including an imposing talus at the southwest. A circuit wall once extended from the outcrop to protect a small adjoining settlement. The medieval fortress is the result of two major periods of construction between the 7th and the 11th centuries; major repairs were undertaken by the Turkish Corps of Engineers in 1977. Atop the north tower are the remains of a Georgian hexaconch church in which a fragment of a 7th-century “bilingual” Greek-Armenian inscription was reused in the foundation. This Georgian church was built sometime between the 9th and 10th centuries. Inside the north tower is the tomb of a Muslim saint, Mişrî Zenūn. Late-antique and medieval churches as well as fortresses are located in the hills surrounding the Oltu-Penek valley at Cücürüs, Körolu, Olur, Kamhis, Sağoman, Olan, and nearby Kız.
During the Ottoman period the Arslan Pasa Mosque was built in 1665 by Arslan Pasha together with his grave. It is a domed structure with a pencil minaret. Nearby is the 14th century Muslim tomb/kümbet, of Misri Zunnun located. During the Russian rule (1878-1914) a new church was built which is now partly ruined, some of its stones could have come from the medieval Bana Cathedral. In the village of Gaziler there is a 12th-century Saltukid castle with a small Ottoman mosque build in 1784.
In the late 19th century the district of Oltu was mainly Turkish (70% in 1897) while the small town of Oltu was mixed.  The district became part of the Russian Empire in 1878. The Russian authorities held a census in 1897 showing that the district of Oltu, including the town, had 31.519 inhabitants of whom 20.719 were Turks, 3.505 Kurds, 3.125 Armenian, 2,704 Greek and 1.038 Slavic.
The town of Oltu itself had 2.373 inhabitants of whom 709 were Slavic, 101 Greek, 1.056 Armenian and 357 Turks. Most of the Slavs were recent settlers coming after 1878. Many of them could be soldiers because there were very few females among them.
Oltu is situated in the Oltu Brook Valley, a tributary of the Çoruh River, in the northeastern part of Turkey. Outside the valley the topography is mountainous, with ample mountain forests. The highest hills are Akdağ of 3,030m and Kırdağ of 2,000m. Annual average temperature is 10.2°C.
Oltu is famous for its Oltu stone or Oltu Gemstone, known as Black Amber with dull-bright black color and carved to produce jewelry, rosary beads, key-chains, pipes and boxes.
- "Area of regions (including lakes), km²". Regional Statistics Database. Turkish Statistical Institute. 2002. Retrieved 2013-03-05.
- "Population of province/district centers and towns/villages by districts - 2012". Address Based Population Registration System (ABPRS) Database. Turkish Statistical Institute. Retrieved 2013-02-27.
- (Armenian) Hakobyan, Tadevos Kh. «Օլթի» (Olti). Armenian Soviet Encyclopedia. vol. xi. Yerevan: Armenian Academy of Sciences, 1986, pp. 527-528.
- Edwards, Robert W., “Medieval Architecture in the Oltu-Penek Valley: A Preliminary Report on the Marchlands of Northeast Turkey” (1985). Dumbarton Oaks Papers XXXIX. Washington, D.C.: Dumbarton Oaks, Trustees for Harvard University. pp. 15–37, pls.1–18, 57–71. ISBN 0-88402-143-2.
- Georgian Soviet Encyclopedia, 7th volume.
- Hovannisian, Richard G. (1996). The Republic of Armenia, Vol. IV: Between Crescent and Sickle, Partition and Sovietization. Berkeley: University of California Press. pp. 182–190. ISBN 0-520-08804-2.
- Sinclair, T.A. (1990). Eastern Turkey: An Architectural & Archaeological Survey, Volume II. Pindar Press. ISBN 9780907132325.
- "Демоскоп Weekly - Первая всеобщая перепись населения Российской Империи 1897 г. Распределение населения по родному языку и уездам. Российской Империи кроме губерний Европейской России". Демоскоп Weekly. Retrieved 22 April 2015.