This paper presents a study of the Aqueduct of Salona, capital of the Roman province Dalmatia, built in the 1st century bc. The aqueduct once transported water from the Jadro River spring, situated approximately 3 km east of the city. Even though it was built for a city of 15 ha in size, two centuries later it succeeded in managing the supply and demand of water for a city of 73 ha. In the 7th century Salona was destroyed by the Avars and Slavs, and consequently, the aqueduct ceased to function. Due to intensive exploitation of marlstone and uncontrolled 20th century urbanization, some of the aqueduct's sections have been destroyed. Research on Salona and its aqueduct started as early as the mid-19th century, however, the aqueduct and its route have never been systematically explored until 2014–2015. This paper provides the results and findings of the latest research including the following: the route of the aqueduct, its longitudinal profile, capacity and typical cross-sections, and the method of construction in different terrain conditions. The channel was built in the usual manner in accordance with the practice of Roman builders, using local materials.
The earliest traces of human presence in the Salona area date back to the late Bronze Age (Šuta 2012). During the Iron Age, the Jadro River mouth, with the isle Vranjic, was an important port and the point of contact of the indigenous Illyrian tribe the Delmatae with the Mediterranean world. Delmatian fortified settlements were situated on elevated positions around the port (Katić 2010).
As the capital, Salona was the administrative centre of great Dalmatia – in that time 7.5 times bigger than today. During the rule of Augustus and Tiberius, a regional road network was built, starting from Salona. The economy was based on agriculture and farming, but also on fishing, crafts and maritime affairs. The Dalmatian inland (present-day Bosnia and Herzegovina) was known for its iron, lead and silver ore wealth, which were exported through Salona port. Estimates have been made by various Salona researchers about its population, 40,000–60,000 inhabitants, on the basis of the size of the forum, the cavea of the amphitheatre, and the capacity of the aqueduct (Suić 1976; Zaninović 1980-81; Cambi 1991; Božić 1997).
The development of the city was followed by the development of infrastructure including water supply, surface water drainage and regulation of water inside and outside the city. Based on the inscriptions on lead pipes, C.JUL.AN.X. (Carrara 1991) ‘Iulius Eucarpus and C. Iulius Xantus’ (Gerber 1917), the Salona aqueduct can be dated to the time immediately after Salona gained the status of a colony in the 1st century bc (Abramić 1991; Kähler 1991). It is considered that the aqueduct ceased functioning in the 7th century, after it was damaged during the siege of the city (Novak 2005). According to Bulić, in the late 19th century, slabs from Salona aqueduct were taken to cover the channel of the Diocletian aqueduct which was under reconstruction (Cambi 1991). Over 1,000 m of the Salona aqueduct channel was destroyed in the 20th century due to intensive exploitation of marl for cement production in the local factories. Residents of this area also contributed to the destruction of the ancient aqueduct by demolishing the parts of the channel on their private plots.
Salona city water supply, surface water drainage and sewerage were first described by Gerber in 1917 (Gerber 1917). He described the way the channel was built, its dimensions and observed calcification on its walls that showed the limit to which the channel was filled. Based on the section of water in the channel and the slope of 0.2%, he calculated, for the first time, the potential capacity of the aqueduct, which according to him was 0.140 m3 per second, i.e. 12,000 m3 per day.
Danish architect Ejnar Dyggve carried out research on the Salona aqueduct as a part of his work in Salona from 1922 onwards. From the late 20th century to the present-day, the most engaged archaeologists on the Salona aqueduct have been Jasna Jeličić-Radonić and Miroslav Katić, from the Conservation Department in Split (Katić 1999). New research conducted in 2014–2015 attempts to give, for the first time, a complete reconstruction of the Salona aqueduct from the spring to the city.
RESULTS OF AQUEDUCT RESEARCH 2014–2015
Characteristics of the aqueduct route
Thanks to the new research the aqueduct route from the Jadro River spring to the north-east corner of the oldest centre of Salona has been defined for the first time. The assumption that the route meanders following the configuration of the terrain proved to be correct. No significant structures were built on the route, such as bridges, tunnels or siphons to span the valleys to shorten the route. The route of the aqueduct conforming to the terrain was a common practice in Classical Antiquity, and was chosen because it was seen as the most economical construction technique (Samiotakis et al. 2004). The reason for this is the adequate elevation of water intake at the Jadro spring (33 m a.s.l.), which allowed gravitational water supply to the city of Salona whose highest point of terrain is at 10 m a.s.l.
Structures on the route of the aqueduct
Every aqueduct, i.e. the main supply channel, usually has two main structures: water intake at the spring, river or lake and distribution tank at the entrance to the city (castellum divisorium), i.e. at the beginning of the city's water supply network (Hodge 2002; Monteleone et al. 2007). There are other structures along the channel route, necessary for stabilization and protection of the channel and its maintenance.
Characteristics of the channel
Only two openings of rectangular shape have been found so far on the whole aqueduct route, which were used for revision, cleaning and repairing of the channel, one in probe 6 (Figure 12) and the other in Salona west of the Episcopal centre. Considering the length of the channel, there should have been more shafts. Until now, no floodgates have been found. The settling tanks or settling basin, which was set at the bottom of the aqueduct channel, have not been found. Natural spring water has a small amount of suspended solids, therefore, there was no need for sedimentation.
On the channel walls, in a number of places, calcification-sinter is preserved (calcite bound to the walls and channel bottom), which clearly shows the level of the water in the channel and the quantity of water that constantly flowed through it. Where the channel is more distant from the Jadro spring there is more calcification. This is a normal feature of karst water. The small accumulation of sinter incrustation was found in the conduit due to the fact that the aqueduct was functioning for six centuries. Sinter-accumulation roughened the channel and increased the contact area for a given amount of water, and it is, therefore, presumed that there were no significant retardations of flow.
Capacity of the channel
The Salona aqueduct was built in the 1st century bc. At the beginning it supplied a city of about 15 ha in size and at the end a city of about 73 ha. It was completely built as a gravity supplier with free water table.
The dimensions of the Salona aqueduct channel range from 62 to 100 cm in width and from 72 to 121 cm in height. These dimensions are similar to the dimensions of the channel flow section of the Diocletian Aqueduct: 60 cm in width, and 120 cm in height (Marasović et al. 2014). Changes in size and construction techniques were conditioned by local features of the terrain. The channel follows the contour lines in the entire length and is built on the terrain or is shallowly buried beneath the ground surface. Where the channel is laid under the ground it is about 1.2 m high and about 60 cm wide. Where it is built on the ground it is wider and its height is slightly less. The channel does not have any significant structures such as bridges or siphons, except for a small bridge before the entrance to the old city. It appears that the route and the construction of the channel without major facilities was an optimal solution hydraulically and economically. The average longitudinal channel slope is about 0.36%, however the average slope at the longest watercourse is 0.25%. The rate of flow was greater than 0.8 m/s due to the channel slope, the settling of suspended solids was prevented, and water was conveyed from the spring to the city in a short period of time of ca. 2 h. Fresh water, at a water temperature of ca. 15 °C, was conveyed to the city.
This aqueduct was built entirely from stone slabs, which was not a common practice. The only known similar aqueduct is the one in Toda (Riera 2006), nevertheless, similar aqueduct construction can be seen at the channel of the Roman aqueduct Anio Vetus (Ashby 1991). More than 20,000 stone slabs, 300 kg to 3,000 kg, were required for its construction. The stone slabs had to be cut, transported, and implemented. Good organizational skills, skilled workers, and a large amount of time were necessary for the execution of the construction works.
The Salona aqueduct illustrates good engineering practice. The channel or the water supply system was in function for more than six centuries, which clearly demonstrates the quality of construction and even more the quality of maintenance and management of this important urban water system. The quality of water was good, partially due to effective water pollution prevention. It is once again shown that the Romans made sure to provide sufficient quantities of quality water to their cities in order to strengthen the sustainability of life in the cities. This paper presents the current, preliminary results of a 1-year study. Analysis of available data and archaeological research will continue in order to study in more detail this valuable historical hydro-technical facility, as well as the Roman practice of construction of urban water systems on the east coast of the Adriatic Sea.
This paper is based upon work primarily supported by the Croatian Scientific Foundation under HRZZ Research Project IP-11-2013.