In 1358. Dubrovnik acquired Pelješac and erected a monumental defensive system, the largest fortification and urban achievements in Europe at the time.Dubrovnik invested huge sums of money and employed the following buiders: :Mihač and district Bunić among the first local designers: the Italians Onofrio from Naplesi and Bernandin from Parma, the French Olivier and the Florentinei Michelozzo, and stone masters Juraj Dalmatinac and Paskoje Miličević from Dalmatia.It was completed at the end of 15th century.During the first thirty years, the defensive walls, the longest in Europe, were built from one side of the peninsula to the other.Then two small fortified towns were erected according to plan, Ston on the north and Mali Ston on the south, for the purpose of housing people for guarding the borders and working in the saltpans.Pelješac is devided from the mainland, above the steep western slopes, by the Big Wall. These walls go across the hill in a double row with a total lenght of 5.5 kms and are protected by some 40 towers and 5 forts, the strongest being Bartolomija at the highest point, named for the saint-protector of arms. Diverging walls encompass Mali Ston on the north with the tower of Koruna, consisting of four smaller towers resembling a crown, from which it gets its name('kruna'=crown).Ston, larger and historically more important, has the same defence system, and the geometrical arrangement of its saltpans reflects a similar pattern in the town and fields.The town is enclosed with 1 km long wall in the shape of a pentagon with the semicircular tower of Podzvizd on top. Previously this wall also had an outer wall with ditches, which followed the palisades to the saltpans along the bay.It ended immediately in front of the town where the port was protected by a large tower on Veliki Kaštio(1357), a crucial point of this fortification.