This mosque was built in 1296 AD and is one of the oldest buildings in Tlemcen. It was named after the scholar and judge Abi al-Hasan Ali. This mosque is considered one of the jewels of Islamic architecture in the city, as it has a unique architectural character and is decorated with beautiful Islamic inscriptions and decorations, in addition to being classified as one of the most beautiful mosques in the world. The Abu al-Hassan Mosque witnessed many events over time, and then it was converted into a museum of Islamic calligraphy and a school at the same time.