Bourgas is a successor of the small Roman town of Deultum (later named Develt), founded by Emperor Vespasian as a military colony for veterans. Besides Deultum, the present-day city expands over the area of three other ancient settlements, i.e. Kastiacion, Skafida and Rossokastron. In the Middle Ages a small fortress called Pirgos was erected in the place and was most probably used as a watchtower. It was only in 17tn century that a town named Ahelo-Bourgas grew in the present-day area of the city. This, renamed into Bourgas, had only about 3,000 inhabitants at the time of the Liberation. Soon it became the centre of the Southern Black Sea coast, and a city of well developed industry and trade. A number of oil and chemical works producing more than 30 products were gradually built. Salt and iron are also mined here and traded far beyond the borders of the country. In 1903 the railway station in Bourgas started functioning as well, giving an additional boost to the city's expansion.