Mazara del Vallo is a city and comune in the province of Trapani, southwestern Sicily, Italy. It lies mainly on the left bank at the mouth …Mazara del Vallo is a city and comune in the province of Trapani, southwestern Sicily, Italy. It lies mainly on the left bank at the mouth of the Mazaro river. It is an agricultural and fishing centre and its port gives shelter to the largest fishing fleet in Italy. The city is also one of the most historically significant in Sicily.