Such examples are the fortification structures excavated at a salt-producing town near Provadiya and a fortified settlement now in Ticha Dam, near Shumen, both belonging to the 5th millennium BC. Archaeologists interpret these two sites as early evidence for a stratified society whose wealth and resources attracted incursions and invasions.

Discovering new fortifications sounds great, but most of the fortresses in the Bulgarian lands are in a condition that can excite only an archaeologist. Few have survived in a state fit for Instagrammable photos.

We introduced some of those in Vagabond's previous issue, now it is time to add other mighty ruins of forts built, abandoned, rebuilt and abandoned again from Antiquity to the Ottoman period.

Vidin Fortress

Bulgaria's only completely preserved citadel has a deep moat which could be filled with water from the Danube, massive walls and strong turrets. It stands on the site of an earlier Roman fortification, and in the 10-14th centuries was a major Bulgarian stronghold, becoming, in the second half of the 14th century, the capital of the Kingdom of Vidin.

Under the Ottomans, between the 15th and the 17th centuries, the fortress often came under attack by the Austrians, the Hungarians and the Wallachians, and was reconstructed according to the contemporary rules of fortification. By the 1880s, however, it had long become a shadow of its former self, and was used mainly as a prison. Still, the citadel fared well during the 1885-1886 Serb-Bulgarian war, when it was besieged by Serbian forces.

Vidin Fortress is also the subject of arguably Bulgaria's most feminist legend. It tells of three aristocratic sisters who built three fortresses in the region. The middle and the younger sisters were married to evil men who squandered their fortunes. The eldest one, Vida, never married, ruling happily in her stronghold and taking good care of her subjects. When she died, the castle was named after her.

Belogradchik Fortress

For visitors, the red Belogradchik Rocks are one of the most astonishing natural phenomena in Bulgaria. The Romans, however, had an eye for something completely different. The high rocks were the perfect place to build a fortification guarding the route from the Danube to the Aegean.

A number of later rulers who controlled the area thought so too. In the 14th century, the Bulgarian lords of nearby Vidin rebuilt the fortress. The Ottomans were happy for centuries with this one, until the Serbian Uprising of 1804 (which eventually led to Serbia's independence). In 1805-1837, the Belogradchik Fortress was completely reconstructed by French and Italian engineers.

This is the layout tourists see today, with two bastions and a citadel, picturesquely huddled between the highest pinnacles of the Belogradchik Rocks.

Asenova Fort

Located at the northern end of a route through the Rhodope Mountains connecting the Thracian Plain with the Aegean, Asenova Fort was built more on more than one occasion. The ancient Thracians were the first to fortify the cliffs where the River Chaya flows from the mountains, and later the Byzantines constructed a mighty castle, in the 9th century. The citadel became an important and much contested military outpost between Bulgaria and Byzantium. It was under the rule of Bulgarian King Ivan Asen II when it was completely rebuilt, in 1231, and promptly named after him. The fortress was abandoned in 1410, after the Ottomans established control of the region.

The only part of the fort to survive almost intact from the Middle Ages is St Petka Church. Now it is the most beautiful part of Asenova Fortress, together with the vista of the northern slopes of the Rhodope and the Thracian plain.

Matochina Fort

One of the most spectacular Bulgarian fortresses is a mass of stone masonry rising among the hills of this no-man's land on the border with Turkey. The fortress, whose ancient name was probably Boukelon, has seen a lot; the fateful battles of Romans and Goths in 378, and of Bulgarians and the Holy Roman Empire in 1205, near Hadrianopolis (today Edirne), are only the two more famous events in a long list of local clashes.

Under the Ottomans the fortress was abandoned and gradually fell into disrepair. By the 17th century it was nothing more than a hunting ground for the sultans.

Under Communism, Matochina was completely off limits to anyone without a special permit because it sits right on the border with Turkey. It is accessible now and well worth a visit.

Mezek Fort

On one of the last hills of the Eastern Rhodope near Svilengrad stands one of the best preserved mediaeval fortresses in Bulgaria. It was built at the turn of the 11th-12th centuries during the reign of Byzantine Emperor Alexios I Komnenos and saw much action in the 13th-14th centuries, when the region was hotly contested by Bulgarians, Byzantines, the Holy Roman Empire and the Ottomans. The walls were almost intact until 1900, when many of the stones were taken to Svilengrad and used to build military barracks.

The fortress was declared a site of historical importance as early as 1927, but this did not protect it from becoming an actual military site during the Cold War. A bunker was constructed at the tip of the fortification that overlooks the surrounding plain, because Svilengrad was on the border with NATO-members Turkey and Greece.