The al-Qamus (حصن القموص) was the name of one of the fortresses of al-Rabi ibn Abu al-Huqayq, Banu Qurayza situated near Khaybar. The fortress was attacked by Muslim forces and it fell to Muslim forces in 629/30 CE. It was after this event that Muhammad married Safiyyah bint Huyayy. Although traditionally it is believed to be the Qamus fort but there is no direct archaeological evidence. The Khaybar was still inhabited by Jews, as late as the late 7th century CE, who pioneered the cultivation of the oasis.

Qamus Fort was an ancient fortress in the Jewish stronghold of Khaybar oasis. Situated north of Medina, it was takenover by Muslim forces in the Battle of Khaybar. It is located on an elevated ridge, overlooking the old Khaybar. Before the rise of Islam, this fortress town had been inhabited by Jewish tribes; it fell to Muslim forces in 629 CE.

In the broader landscape of early Islamic consolidation of territorial security, al-Qamus represented the pinnacle of Khaybar's defensive system, a fertile oasis spanning about 56 square kilometers fed by springs and wadis amid the volcanic Harrat Khaybar. The oasis supported a population exceeding 20,000 inhabitants, including around 2,000 warriors proficient in both agriculture and warfare, who amassed significant wealth through farming, trade, and arms acquisition. As part of a constellation of seven to thirteen forts—among them Na'im, Katibah, Nastat, Shiq, Watih, and Sulalim—al-Qamus functioned not merely as a refuge but as a hub for coordinating resistance, with underground passages linking it to adjacent strongholds to facilitate resource transfers during sieges. Its fall in 629 CE marked a turning point in Muhammad's campaigns, securing the northern Hijaz and integrating the area's economic resources into the nascent Muslim polity, while the site's later repurposing under the Saudi monarchy highlighted its enduring strategic value.

circa 629 CE

Muslim invasion was not the first time Khaybar was sacked, previously in 567 CE, the area was invaded and vacated of its Jewish inhabitants by the Ghassanid Arab Christian king al-Harith ibn Jabalah. He later freed the captives upon his return to the Levant. A brief account of the campaign is given by Ibn Qutaybah, and confirmed by the Harran Inscription.

The historical trajectory of al-Qamus traces back to uncertain origins of Jewish settlement in northern Arabia, though by the sixth century CE, the oasis had become a prosperous enclave inhabited by tribes such as Banu Nadir and Banu Qurayza. In 567 CE, the Ghassanid king al-Harith ibn Jabalah, an Arab Christian ally of Byzantium, invaded Khaybar, expelling its Jewish residents and seizing captives, only to release them upon returning to the Levant, as documented by Ibn Qutaybah and corroborated by the Harran Inscription. Resettlement followed, fortifying the area against further incursions, until tensions escalated with the rise of Islam; Khaybar's Jews, having been exiled from Medina after events like the Battle of Uhud, allied with Arab tribes and foreign powers, including potential overtures to Persian and Byzantine emperors, prompting Muhammad to view the oasis as a persistent threat post the 628 CE Treaty of Hudaybiyyah.

In 7 AH (629 CE), Muhammad mobilized 1,600 infantry and 200 cavalry—limited initially to Hudaybiyyah participants for booty rights—advancing secretly to isolate Khaybar from allies like the Banu Ghatafan. The month-long siege commenced with Na'im's capture, where Mahmud bin Maslamah Ansari was martyred by a stone projectile, before focus shifted to Al-Qamus under its chief, Kinana ibn al-Rabi (or in some accounts, Ibn Abil Haqiq). Initial assaults faltered: Abu Bakr and Umar led charges but retreated amid fierce resistance from catapults and arrows. Muhammad then entrusted the banner to Ali ibn Abi Talib, recently recovered from illness, who engaged the Jewish champion Marhab in a duel at the fort's gates; after exchanging verses—Marhab boasting of his prowess, Ali retorting with his lion-like ferocity—Ali cleaved Marhab's helmet and skull with a single blow, paving the way for the garrison's rout. The 13- to 19-day blockade ended with the fort's surrender, yielding captives including Safiyyah bint Huyayy, whom Muhammad married after her manumission.

Total casualties numbered 20 Muslims and 93 Jews, leading to a pact allowing Jews to farm under Muslim oversight without jizyah, though later caliphs like Umar expelled them in the mid-seventh century. By the early twentieth century, King Abdulaziz al-Saud annexed Khaybar, reconstructing Al-Qamus as an emirate headquarters.

circa 629 CE

Physically, Al-Qamus perched atop a high basalt ridge, locally termed the "Mountain of Jews," rising like a ship amid encircling palm seas, its elevated position enhancing surveillance via watchtowers over the wadi floors below. Constructed from local stone on volcanic outcrops, the fort integrated homes, storehouses, stables, and defensive walls, with family clans occupying distinct sections amid cultivated fields. Archaeologically, while the visible ruins—spanning dense wall networks and structures abandoned by the 1980s—align with Islamic-period settlements from the seventh century onward, no direct evidence confirms the current edifice as the original seventh-century site; instead, it associates with broader oasis remnants, including Abbasid-era expansions like Kharayib al-Sihlah's monumental buildings and mirabad enclosures for date processing, dated via ceramics, glass, and radiocarbon to the ninth through twelfth centuries.

This probably is a modern structure, built on a basalt rock, Khaybar. Locally known as the "Mountain of Jews" the fortress of Qamous is situated on top of a high ridge in the Khaybar region of Saudi Arabia. Before the advent of Islam in the 7th century CE, indigenous Arabs, as well as Jews, once made up the population of Khaybar, although when Jewish settlement in this part of the northern Arabia began is not known with certainty.

circa 629 CE

The oasis of Khaybar had several fortresses or redoubts containing homes, storehouses and stables, like this one. Each fortress was occupied by a separate family and surrounded by cultivated fields and palm-groves. In order to improve their defensive capabilities, the settlers raised the fortresses up on hills or basalt rocks. The Qila Qamus and the surrounding dwellings were rebuilt as the headquarters of the Emirate, when it was annexed by King Abdulaziz al-Saud (عبد العزيز آل سعود).