Jabal Nuqum rises about 500 metres above Sanaa. According to the 10th-century writer al-Hamdani, the mountain was the site of an iron mine, although no trace of it exists today; he also mentions a particular type of onyx which came from Nuqum. Muhammad ibn Zakariya al-Razi described a dam located at Nuqum; its location is not known. This dam probably served to divert the waters coming down from the western face of the mountain and prevent them from flooding the city of Sanaa. Such a flood is known to have happened in 692 (73 AH), before the dam was built, and it is described as having destroyed some of Sanaa's houses. Despite its proximity to the city, Jabal Nuqum does not appear to have been fortified until 1607 (1016 AH), when a fort was built to serve as a lookout point to warn of potential attackers. The main mountain stronghold during the middle ages was Jabal Barash, further to the east.