<P> There was no standard currency throughout the realm, but several forms were prominent by region . The Sahelian and Saharan towns of the Mali Empire were organised as both staging posts in the long - distance caravan trade and trading centres for the various West African products . At Taghaza, for example, salt was exchanged; at Takedda, copper . Ibn Battuta observed the employment of servants in both towns . During most of his journey, Ibn Battuta travelled with a retinue that included servants, most of whom carried goods for trade . On the return from Takedda to Morocco, his caravan transported 600 female servants, suggesting that indentured servitude was a substantial part of the commercial activity of the empire . </P> <P> Gold nuggets were the exclusive property of the mansa, and were illegal to trade within his borders . All gold was immediately handed over to the imperial treasury in return for an equal value of gold dust . Gold dust had been weighed and bagged for use at least since the time of the Ghana Empire . Mali borrowed the practice to stem inflation of the substance, since it was so prominent in the region . The most common measure for gold within the realm was the ambiguous mithqal (4.5 grams of gold). This term was used interchangeably with dinar, though it is unclear if coined currency was used in the empire . Gold dust was used all over the empire, but was not valued equally in all regions . </P> <P> The next great unit of exchange in the Mali Empire was salt . Salt was as valuable, if not more valuable, than gold in sub-Saharan Africa . It was cut into pieces and spent on goods with close to equal buying power throughout the empire . While it was as good as gold in the north, it was even better in the south . The people of the south needed salt for their diet, but it was extremely rare . The northern region on the other hand had no shortage of salt . Every year merchants entered Mali via Oualata with camel loads of salt to sell in Niani . According to Ibn Battuta who visited Mali in the mid-14th century, one camel load of salt sold at Walata for 8--10 mithqals of gold, but in Mali proper it realised 20--30 ducats and sometimes even 40 . One particular source of salt in the Mali Empire was salt - mining sites located in Taghaza . Ibn Battuta had written that in Taghaza there were no trees and there is only sand and the salt mines . Nobody lived in the area except the Musafa servants who worked to dig the salts and lived on dates imported from Sijilmasa and the Dar'a valley, camel meat and millet imported from the Sudan . The buildings were constructed from slabs of salt and roofed with camel skins . The salt was dug from the ground and cut into thick slabs, two of which were loaded onto each camel where they would be taken south across the desert to Oualata and sold . The value of the salt was chiefly determined by the transport costs . Ibn Battuta mentions that the value of salt increased fourfold when transported between Oualata and the Malian capital . </P> <P> Copper was also a valued commodity in imperial Mali . According to the records of Ibn Battuta, copper which traded in bars was mined from Takedda in the north and traded in the south for gold . Contemporary sources claim 60 copper bars traded for 100 dinars of gold . </P>

Why was salt considered as valuable as gold in ancient mali
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