Pollen analysis
Under Justinian the walls of Serdica, Ulpianum and many other towns were repaired. He also had hundreds of small forts erected along the Lower Danube, at mountain passes across the Balkan Mountains and around Constantinople. Inside these forts small churches and houses were built. Pollen analysis suggest that the locals cultivated legumes within the walls, but no other trace of agriculture have been identified. They were supplied with grain, wine and oil from distant territories, as it is demonstrated by the great number of amphorae unearthed in these sites which were used to transport these items to the forts. Most Roman towns and forts in the northern parts of the Balkans were destroyed in the 570s or 580s. Although some of them were soon restored, all of them were abandoned, many even "without any signs of violence", in the early 7th century.