Although it is one of the main archaeological sites in Oman, the medieval port of Qalhat, near Sur in Ash-Sharqiyah Governorate, has long remained poorly documented. The extensive research initiated in 2008 by the Ministry of Heritage and Tourism (at the time, Heritage and Culture) shed striking light on the history of this famous harbour city, which was the twin capital of the Kingdom of Hormuz from the 13th to the 16th century. Surface surveys and excavations have revealed the plan and chronology of the city and its different districts. Mosques (including the Great Mosque built by Bibi Maryam around 1300) and other religious buildings, fortifications, and water supply systems have been identified and studied. The craft and economic activities of the city and the regional and international commercial links of the port have been reconstructed, as well as the daily life of its inhabitants, revealing the wealth and cosmopolitan character of this ancient Omani metropolis. All these results highlighted the Outstanding Universal Value of the site and eventually led to the inscription of Qalhat on the UNESCO World Heritage List in 2018.