Underwater archaeology is the field of study that seeks to unravel the mysteries of history from ruins lying at the bottom of the sea. Born in the Mediterranean in the 1960s, this new branch of archaeology reveals unique episodes from our past. This article introduces the fascination behind sunken shipwrecks - a unique type of ruins - and the significance of researching them.

Archaeology is the study of excavating and researching ruins - the traces of past human lives - to understand our forgotten past. Some of you may have already known about a specific field of archaeology called underwater archaeology.
With its beginnings in the excavation and research of ancient shipwrecks in the Mediterranean in the 1960s, underwater archaeology is now regarded as an essential field of archaeological research in many countries around the world. Why is this a field of interest? It is because the archeological sites which serve as the research subject exist in unique underwater environments. The most significant feature of underwater archaeology is how well the ruins are preserved. For example, if a ship from the ancient Roman period 2,000 years ago ran aground in a storm and sank onto a sandy seafloor, the weight of the cargo and the currents would cause the sand to cover it, creating a unique environment where the shipwreck is buried in the sand. As a result, the environment surrounding the wreck is free of oxygen, preventing marine organisms and bacteria from proliferating. Consequently, even organic materials such as wood can be preserved in almost perfect condition for 2,000 to 3,000 years or more. It is not uncommon for shipwrecks to be discovered in excellent condition, as if they had sunk just yesterday. Therefore, many underwater ruins excavated from the seafloor possess more valuable information than those on land, often having high academic value. This is why underwater archaeology attracts so much interest among Western archaeologists.

The most commonly discovered form of underwater ruins is sunken ships. According to estimates by the United Nations Educational, Scientific and Cultural Organization (UNESCO), which manages World Heritage registrations, there are at least 3 million sunken ships of historical value worldwide which sank more than 100 years ago. However, only a few tens of thousands of sunken shipwrecks have been discovered and known to exist, and only a few hundred have been under academic investigation. In this sense, underwater archaeology can still be considered an unexplored field of study. When examining the archaeology of sunken shipwrecks, the main subjects of research are the cargo and the hull of the ship. If the sunken ship was a merchant or transport ship of its time, the cargo is often excavated as part of the wreck. These cargoes were not merely transported from port A to port B. Instead, goods collected from various nations and civilizations in each region were gathered at port A, loaded onto the limited space onboard ships, and transported to another region's port B, where they were further distributed throughout that region's countries. In other words, sunken shipwrecks encapsulate the distribution and trade conditions between civilizations and nations of that time. Excavating and researching sunken shipwrecks enables us to understand the distribution and economic systems of the era in which the ship was in operation. Of course, this understanding is based on the premise that underwater ruins are well-preserved, but it is also precisely because these unique ruins are “ships” - an aggregation of inter-state distribution systems - that so much historical insight can be gleaned.
In addition to the cargo, the sunken ship's hull is also an essential subject of archaeological research. Professor George Bass (1923-2021), known as the father of underwater archaeology, was quoted as saying, "Before there were farmers or shepherds, there were seafarers." This statement indicates the importance of ships in the birth and prosperity of human civilization, as evidenced by the fact that humans had already reached remote islands and continents such as Australia long before the advent of agriculture. By studying the remains of ships, we can learn about the technological levels of civilizations and nations at the time. For contemporary archaeologists, studying the structures of ancient ships is synonymous with future archaeologists studying the technology of 21st-century nuclear submarines and the International Space Station to understand our current technological level.

Underwater archaeology faces several difficulties not encountered in terrestrial archaeology. The most challenging is time constraints. Underwater archaeology starts when ruins are discovered and proceeds to excavation and documentation; then, research is performed based on the information obtained. This research is the core of archaeology. However, to collect research materials (archaeological information), the ruins must be carefully excavated, and as much information as possible about the unearthed structures and artifacts must be recorded in detail. In other words, sufficient time must be spent on excavation and documentation to conduct better research.
In the case of underwater archaeology, the excavation site is underwater, so work must be done while scuba diving. Underwater, the compressed air we breathe causes nitrogen to accumulate in our bloodstream above normal, which can lead to potentially lethal decompression sickness when surfacing as pressure decreases, forming bubbles and blocking the blood flow. Therefore, the time spent on underwater work is much shorter than that spent on terrestrial archaeological excavations. For example, at a depth of 30 meters, diving work is limited to about 30 minutes per session, two times a day, for safety reasons. Recently, photogrammetry (measurements using photography) and digital 3D modeling technology have helped improve this situation¹. Moreover, underwater archaeologists worldwide are putting these technologies to the test to verify the usefulness in various applications.

Despite being surrounded by the sea, Japan has unfortunately not been as active in underwater archaeology research as other countries. This can be attributed to the extremely few cases where underwater sites fall under "archaeological and/or historical subsoil," to which the Law for the Protection of Cultural Properties - which was enacted to prevent the destruction of archaeological sites during area development - is applicable². As a result, underwater ruins have not been subject to preliminary investigations during development projects. Their existence has not been widely known due to destruction by seawall construction and land reclamation projects. However, from a different perspective, underwater archaeology in Japan is still an immature field of study. If the existence of underwater ruins and the historical value and importance of the knowledge gained from their investigation are properly recognized, Japan has the potential to become a leading nation in this field within a few years.
This is because Japan has a world-class system for protecting and managing terrestrial ruins and a top-level standard of archaeological research in the world. Each municipality has a Buried Cultural Properties Division staffed with experienced archaeologists well-versed in the history of local terrestrial ruins³. There are approximately 6,000 archaeologists working as public servants throughout Japan. If even one in 100 of them were to obtain a diving license and begin investigating underwater ruins, the field of underwater archaeology in Japan would flourish rapidly. What kind of history has Japan, a country surrounded by the sea, experienced in its interactions with other countries? The keys to solving this mystery await our discovery at the bottom of the sea. (End)

2. Akifumi Iwabuchi, "Marine Cultural Resource and the UNESCO Convention on the Protection of the Underwater Cultural Heritage,"
No. 344 of this newsletter (December 5, 2014)
3. Kohei Sugiyama, "What Land-based Archaeologists Are Seeking among Our Underwater Cultural Heritage,"
No. 467 of this newsletter (January 20, 2020)