The name of the city, Harran, has been used continuously and with little modification since ancient times and is mentioned in the earliest known records of the city. It appears in early cuneiform records of both the Sumerians and Hittites under the name URU.ŠÀ.KASKAL, which was occasionally shortened to KASKAL and transcribed as Ḫarrānu(m).

circa 745 CE

Harran's establishment dates back to the period between the 25th and 20th centuries BCE, and it is believed that it was initially formed as a trading colony by Sumerian merchants from ancient Ur. In its early history, Harran quickly developed into a significant Mesopotamian hub for culture, trade, and religion. The city gained religious and political significance through its association with the moon-god Sin, and several renowned Mesopotamian rulers renovated the moon-temple of Ekhulkhul in Harran. Under Adad-nirari I's rule (1305-1274 BCE), Harran was governed by the Assyrians and became a provincial capital, often ranked as second in importance only to the Assyrian capital of Assur itself. When the Assyrian Empire fell, Harran briefly served as the last capital of the Neo-Assyrian Empire between 612 and 609 BCE.

Following the decline of the Assyrian Empire, Harran maintained its prominence and was influenced by different foreign cultures during its rule under the Neo-Babylonian (609-539 BCE), Achaemenid (539-330 BCE), Macedonian (330-312 BCE), and Seleucid (312-132 BCE) empires. Throughout classical antiquity, the city of Harran was often disputed between the Roman and Parthian (later Sasanian) empires, and in 53 BCE, the Battle of Carrhae, one of the most catastrophic losses in Roman military history, occurred there. Despite the rise and fall of empires, the worship of the moon-god Sin in Harran persisted and lasted until the Middle Ages, with evidence of its existence up until the eleventh century CE. In 640 CE, ancient Harran came under the hegemony of Islam when the Rashidun Caliphate conquered the city, and it became a thriving center of education and science in the Islamic era. The Harran University, the first Islamic university [see note 1], and the Harran Grand Mosque, the oldest mosque in Anatolia, were both established there. Harran served as a capital city twice during the Middle Ages, first briefly under the Umayyad Caliphate from 744 to 750 and then under the Numayrid Emirate from 990 to 1081 CE.

Harran was conquered by the Mongol Empire in 1260, and although it was used as a military outpost under later regimes, it was largely destroyed and abandoned in 1271. For the last five centuries, it has mainly been occupied by local nomadic societies as a temporary settlement. In the 1840s, it began to transition into a semi-permanent village settlement, but it has only recently become a permanent town thanks to advances in irrigation and agriculture. Harran was formerly a Turkish district until 1946, when it was reduced to a sub-district of the Akçakale district. However, it regained its status as a district in 1987.

circa 745 CE

Great Mosque
The Great Mosque of Harran, which is the oldest mosque and represents oldest Islamic architecture in Anatolia (modern day Turkey), was constructed 744-750 CE during the Umayyad period by Caliph al-Marwan II. At the time the historic city of Harran was his capital.

Nothing much survives of the Great Mosque of Harran, also known as the Firdaus Ulu Camii (literally meaning "Paradise Mosque"), except some rubble and the minaret. The wooden stairs of the minaret that disappeared in due course was reconstructed as having 105 steps in compatible with the original one. The masonry of the mosque indicates that it was restored several times throughout its history. A number of notable architectural features still survive to this day, including the thirty-three meters tall minaret (inspect), a fountain (inspect) in the courtyard.

The mosque was not only a religious center, it was also an institution (from the middle of the eighth century towards the end of ninth century CE) of learning that made huge contributions to the the development of not only Islamic empire but the formation of European civilization. Major excavation and restoration efforts have been carried out since 1983 CE.

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Castle
The Harran Castle (Harran Kalesi), also knwon as the Harran Citadel, is a medieval fortress in Harran, Turkey. Although the exact date of its founding is unknown, it is believed to have been originally constructed during the Byzantine rule (4th-7th centuries CE) as a palace, making it much older than its present form suggests. Most of the current structure was built during the Ayyubid Sultanate period around 1200 CE. The castle has an irregular rectangular shape and has dodecagon-shaped towers at each of its four corners. The castle has the dimensions of 90 × 130 metres (295 × 425 feet).

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Medieval University of Harran
The Harran University or the Madrasa of Harran was an institution of higher learning that operated in the Harran during the medieval period. It was active from the 8th century CE and persisted at least until the 12th century CE. It briefly reappeared in the 16th century CE. As the first Islamic institution of its kind, the university had an open intellectual atmosphere, which led to its recognition as a center of science and learning. One of its notable contributions was the translation of documents from Syriac and Greek into Arabic, which played an important role in the transmission and preservation of classical Greek and Syriac learning.

It was during the 8th century CE when Harran University experienced a period of great success, particularly under the rule of Abbasid caliph Harun al-Rashid (786-809 CE). The university played an important role in educating a number of notable Islamic scholars, including Thābit ibn Qurra, al-Battani, Ibn Taymiyyah, and Sinān ibn al-Fatḥ al-Ḥarrānī in subjects like mathematics, philosophy, medicine, and astrology.

It also served as a hub for translating Syriac and Greek documents into Arabic, contributing to the growth of science and learning in Harran. Additionally, al-Rashid facilitated the city's development by constructing a canal from the Balikh River to improve the water supply. While the exact timing is uncertain, it is believed that Harranian intellectuals were introduced to Neoplatonism at some point. This philosophical school may have been introduced by the scholar Thābit ibn Qurra in the late 9th century CE, who could have learned it in Baghdad. Alternatively, it may have been brought to Harran as early as the 6th century CE by Neoplatonists like Simplicius of Cilicia, who sought refuge from persecution in the Byzantine Empire.

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The remains of the ancient city of Harran are usually identified with an ancient city known as Haran in the Hebrew Bible. Mentioned in the Book of Genesis, Haran is said to be the dwelling place of Terah or Tareh, in Islamic tradition known as Āzar and his offspring, as well as a temporary residence of prophet Abraham. Other sections of the Bible refer to Haran as one of the cities and territories subjected to the Assyrian monarchs, as well as one of Tyre's commercial associates.

Although mostly connected with the Biblical city Haran the archaeological activities starting in the 1950s, carried out by a number of archaeologists, however, have yielded inadequate linkage and have failed in shedding light on the city's history before the medieval period or its alleged patriarchal period. The oldest known records of Harran are from the Ebla tablets dating back to around 2300 BCE. It is believed that the name Harran originates from the Akkadian word "ḫarrānum" (feminine), meaning "road," and "ḫarrānātum" (plural).