The origins of Castile Soap can be traced back to The Levant where Aleppo soap makers have been making olive and laurel oil based hard soaps for millennia.
It is commonly believed that the Crusaders brought Aleppo soap back to Europe with them in the 11th century. Following the Crusades, production of this soap was extended to the whole Mediterranean area. The first European soap-making factories were created in the 12th century in Spain (Alicante, Malaga, Carthagene and Castile) and in Italy (Naples, Savone, Genoa, Bologna and Venice) and then, in the middle of the 15th century, in Marseille France, giving birth to Marseille soap.
Info gleaned from Wikipedia