The Great Mosque of Mahdiya is a mosque that was built in the tenth century in Mahdia, Tunisia.
Located on the southern side of the peninsula on which the old city was located, the mosque was built in 916 CE, after the founding of the city within the walls built by the Caliphate on an artificial platform "reclaimed from the sea" as mentioned by the Andalusian geographer Al-Bakri.
The other buildings erected nearby at that time have since disappeared.
Wikipedia https://en.wikipedia.org/wiki/Great_Mosque_of_Mahdiya
Coordinates 35°30'14.371" N 11°4'19.119" E