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St. Thomas Island. (Inset:12th – 14th century monastery)

Sunken Fortress and Ritual Pits Discovered at Holy Island in Bulgaria


Archaeologists in Bulgaria have discovered a Late Middle Ages Byzantine settlement, in the form of a sunken fortress, and a small monastery on Bulgaria’s tiny St. Thomas Island in the Black Sea.

In June 2018, during the initial phase of the island’s first ever archaeological research, a team led by Prof. Ivan Hristov from Bulgaria’s National Museum of History in Sofia discovered the first signs of what they called a “sunken fortress from Ancient Thrace” in waters between the island and the Bulgarian mainland. This area was at one time an isthmus, while the St. Thomas Island used to be a peninsula until the Middle Ages, according to an article in Archaeology in Bulgaria.

St. Thomas Island Archaeological Endeavor

St. Thomas Island in the Black Sea, otherwise known as Snake Island, is part of the Ropotamo Natural Preserve and as such the archaeological explorations were all “carried out under the strict requirements of Bulgaria’s Ministry of Environment and Waters and the project is being wholly funded by Bulgaria’s Ministry of Culture, according to the report.

The Island’s territory totals 0.012 square kilometers (12 decares, or 3 acres) and it lies only 0.2 nautical miles (appr. 370 meters) from the mainland. A 1955 archaeological expedition on Bulgaria’s St. Thomas Island exposed “the ruins of a small church and some auxiliary buildings” but the 2018 archaeological expedition has discovered the remains of an “Early Byzantine (/Late Roman) settlement from the 5th – 6th century AD with “ritual pits” and a small monastery from the 12th – 14th century during the Second Bulgarian Empire (1185 – 1396/1422).”

Ruins of a small monastery which existed in the 12th – 14th century on the St. Thomas Island.

Ruins of a small monastery which existed in the 12th – 14th century on the St. Thomas Island. Image: National Museum of History

Traces of the Thracians

Among the most interesting of the discoveries made so far are reoccurring “Ritual pits” which are found to contain “fragments from ancient amphorae” used by the ancient Thracians in sacrifice rituals starting around the beginning of the 5th century BC, according to a report in Staff at Bulgaria’s National Museum of History in Sofia told reporters that they believed “more Ancient Thracian ritual pits” might be hidden all over the St. Thomas Island. They have also been able to work out from the exposed finds “that a large sea route shrine was located on the St. Thomas Island” which was “a small Black Sea peninsula at the time.” And the reason the shrine was located here in the first place was that it was “right off the ancient road from Sozopol to Constantinople” (called Byzantium at that time), the Museum adds.

A diver from the underwater archaeology expedition shows one of the stone blocks that made up the outer wall of the sunken fortress on what is today St. Thomas Island off the coast of Bulgaria’s Primorsko.

A diver from the underwater archaeology expedition shows one of the stone blocks that made up the outer wall of the sunken fortress on what is today St. Thomas Island off the coast of Bulgaria’s Primorsko. Image: National Museum of History

After “8 years of field research” studying the numerous fortresses and settlements located along the southern Black Sea coast of today’s Bulgaria, or what once was Byzantium’s “Haemimontus province,” Prof. Ivan Hristov has finally published a book entitled Mare Ponticum. Coastal Fortresses and Harbor Zones in the Province of Haemimontus, 5th – 7thCentury AD.” In his tome, he looks at “the Haemimontus province of the Early Byzantine Empire in the Late Antiquity and early Middle Ages.”

Bulgaria the Heritage of the Thracians

Recent Spree in Discoveries

With advancements in technology, the discovery of lost jungle covered kingdoms and sunken cities is becoming more prevalent. It was only last year The Independent reported on the result of an archaeological exploration in search of the ancient city of Neapolis. Working on clues left behind from a Roman soldier and historian named ‘Ammien Marcellin’, who recorded that “Neapolis was submerged by a tsunami in the 4th century AD” a joint Tunisian-Italian archaeological mission went looking for evidence of Neapolis and sent divers down in Nabeul.

After half an hour the divers surfaced and reported that they had found a huge shaped stone that looked manmade, and right they were, for they had glimpsed what would turn out to be the 20 hectare plus mega-archaeological site for the first time in centuries. The archaeological dive team announced to the world’s media that “a vast 1,700-year-old Roman settlement had been discovered off the coast of Tunisia” and the mission’s leader Mounir Fantar told AFP “it was a major discovery” which also confirms Marcellin’s historical account about the city’s cataclysmic fate at the hands of mother nature was spot on.

Top image: St. Thomas Island. (Inset:12 th – 14 th century monastery)          Source: National Museum of History

By Ashley Cowie



With technology increasing allowing new re-discoveries of 'lost' sites, the realizations of sites now under water are phenomonal . Most of what we see to day was up to 30' lower just 600 to 700 years ago. The teams that mapped the Black Sea's depths made astounding discoveries of ancient shorelines, villages & rivers. That water level, at a much more ancient time, was 300' lower than now. The melting ice sheets covering so much land mass & the breakup of the natural dam in the Bosporus changed all that & possibly contributed to the Flood accounts in many cultures. I'll look for more on this site, Thanks !

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Ashley is a Scottish historian, author, and documentary filmmaker presenting original perspectives on historical problems in accessible and exciting ways.

He was raised in Wick, a small fishing village in the county of Caithness on the north east coast of... Read More

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