Salt was not only produced at the coast. Here excavations of salt-working at Uvinza (in Western Tanzania). Later date tanks for storage of brine, as seen, were cut into medieval levels of hearths and wood-ash. (See my webpage on Uvinza).

Medieval Salt Trade.

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Taken from: RESOURCES OF THE OCEAN FRINGE AND THE ARCHAEOLOGY OF THE MEDIEVAL SWAHILI Edward Pollard 2018.

Chittick (1975: 151) observed circular salt-pans in use near Winde, north of Mkadini in the Bagamoyo area. In the surrounding areas he identified ninth–tenth-century Sasanian-Islamic Ware around a low mound, as well as twelfth–thirteenth-century pottery along the creek that he interpreted to be from ancient salt working. He further observed pottery scatters analogous to those at Mkadini (N-Zanzibar), also near the south-west corner of Pate Island and also adjacent to the creek at Kilwa. (ibid.) Showing this kind of side is relatively common along the coast. Changwehela, located roughly 23 km south of Bagamoyo (Chami 1994: 54–5), was another likely site where salt extraction was important. Salt works around the estuaries at Kaole and Mkadini in the medieval period have also been noted by Kleppe (in Lane 2005), in connection with a possible fish-salt trade between Kizimkazi Dimbani (on Unguja) and Kunduchi and Bagamoyo on the mainland.