Liliana Simeonova, Border Control and Shipping on the Lower Danube in Late Antiquity and in the 9th and 10th Centuries
In the days of the Late Roman Empire, the Limes Moesiae followed the course of the Lower Danube. A Roman road, the Via Istrum, ran along the southern bank of the river, linking legion camps, forts, watchtowers, signal posts and stations, from Sirmium (Sremska Mitrovica) to Noviodunum (Isaccea). One of the three units of the Classis Histriae (i.e., the Danube Fleet), the Classis Moesica, secured the border control on the river. It operated not only along the Danube from the Iron Gates to the Danube Delta, but also along the northern Black Sea coast, from the delta to the Crimea. While the Danube Fleet played a significant role in the logistics for the legions by transporting food, weapons and troops it was also a great economic factor, due to the activities of its headquarters, and its ports, marinas and wharfs. The river trade on the Lower Danube covered a wide variety of commodities in the Late Roman period.
Even as the Danube border became gradually weakened in Late Antiquity, the amphorae and fine ware circulation in the Mediterranean world attest to the fact that the Lower Danube was integrated in the extensive network of the Mediterranean long-distance trade routes at least until the beginning of the seventh century. However, as the barbaric incursions into imperial territory intensified, urban life along the southern bank of the river fell into deterioration. From the late 600s to the 960s, the Bulgarians appear to have been making great efforts to keep the delta area under their control. The Byzantines, on the other hand, never gave up on the idea of recovering its control over the mouth of the Danube. Commercial shipping between the Middle and the Lower Danube seems to have been resumed after the Bulgarians and the East Franks concluded a peace treaty in the early 830s. In the 960s, river trade on the Danube appears to have been in full swing. Rock salt from Transylvania, silver, horses and slaves from Bohemia and Hungary were being shipped on the Danube.