Lixus - The Garum Factory

The reason the posh houses were at the top of the hill was that a river level Lixus had an extensive garum factory. Garum was a sauce essential to Roman cooking similar to sauces used in Thailand and Vietnam today , but stronger and more pungent. It was made by taking anchovies and the innards of other pelagic fish and layering them alternatively with salt and leaving it to ferment in the sun for about 3 months. The clear liquid left on the top was drawn off, bottled in amphorae,

 and sold as the best quality garum and the paste, called allec, left at the bottom packed up as a garum substitute for the poor. The actual garum could vary in flavour by adding herbs to the mix but in cooking it was used to make other sauces by mixing with herbs, wine, honey etc. It seems to have been an ingredient in every dish except sweetmeats.
Garum is high in nutrients and monosodium glutamate and umami flavouring. You can buy a similar sauce from Sicily should you wish to try it called Colatura di Alici.
The factory at Lixus had 150 separate troughs carved into the rock to ferment the garum.

 I had thought the sauce would be made from caught fish but in Lixus it was made mainly from anchovies and they seem to have been at least partially farmed. There are a large number of fish ponds

 and a complex system of cisterns and underground tunnels to the river so that the water was renewed at high tide and seawater could be stored.

 The smell must have been awful. presumably this was a job done largely by slaves or the very poor.  
Anchovies are still important in the area today and are served in all the restaurants together with bread and olives whilst you are waiting for your food.