SEOUL, Nov. 4 (Yonhap) -- Traces of shipwrecks believed to date to the Goryeo Dynasty (918-1392) have been found one after another in the waters off Mado Island in Taean, South Chungcheong Province, an area often called an "underwater Gyeongju" for its wealth of maritime archaeological remains.

The discoveries offer a glimpse into cargo ships that transported supplies from the southwestern part of present-day Jeolla Province or from Gyeongsang Province to the capital at the time, potentially helping fill gaps in the history of the Goryeo period.

The National Research Institute of Maritime Heritage said Tuesday that this year's underwater excavation in the Mado waters confirmed the remains of a shipwreck that can be designated as Mado Shipwreck No. 5.

The name refers to the fifth ancient vessel discovered in the Mado waters.

During an investigation last year, the institute found bundles of celadon pieces, a wooden anchor, ropes, rice grains and parts of a hull, all believed to date from around 1150-1175.

The institute began a full-scale investigation in May this year and discovered 54 artifacts, including anchor stones and ropes, in the area where the hull fragments had been found.

An anchor stone is a large stone attached to an anchor to help it sink in the water. Other finds included bundles of rice believed to have been cargo and a bronze jar that may have been used by the ship's crew.

The institute paid particular attention to long, narrow pieces of wood.

A total of 26 wooden tablets bearing inscriptions contained detailed information about when cargo was loaded, when the ship sailed, and its points of departure and arrival.

One tablet, for example, reads, "Twenty seok of rice harvested from the fields, with 18 du each, are being sent." Another says, "Ten seok of beans for the lady's household, with 15 du each, are being sent."

The tablets appear to have served as tags attached to shipments of various grains.

Some of the tablets bear the inscriptions "Year of the Jeongmyo" and "December of the Jeongmyo Year." Considering the dates of organic materials and celadon found alongside them, the year is believed to be 1207.

The institute said the 12th month of the Jeongmyo year would have fallen around January, in the middle of winter, when ships generally did not sail. It added that the vessel most likely set sail in the spring of the following year, 1208.

The tablets identify the cargo's points of origin as Yeongam County and Anro County, names referring to areas that now include Yeongam-eup and Geumjeong-myeon in Yeongam County, South Jeolla Province.

Given that the destination is written as "Gyeong," referring to Gaegyeong, the Goryeo capital, the vessel is believed to have been a government grain transport ship carrying cargo from southwestern Jeolla to the capital.

The institute said the ship appears similar to another Goryeo-era wreck, Mado Shipwreck No. 1.

Mado Shipwreck No. 1 is believed to have sunk off Taean while carrying grain collected from areas including Naju, Haenam and Jangheung in what is now South Jeolla Province, bound for Gaegyeong.

An institute official said one of the newly discovered tablets describes a shipment from Anro County to a person named Song Deuk-deok in Gaegyeong, and that its handwriting and content are almost identical to those on a tablet recovered from Mado Shipwreck No. 1.

The two vessels also appear to share similarities in that they carried cargo from southwestern Jeolla and are believed to have collected their cargo in 1207 before setting sail for Gaegyeong in 1208 and sinking.

Jin Ho-shin, a curator at the institute, said Mado Shipwrecks Nos. 1 and 5 are believed to have belonged to the same fleet and sunk together after encountering bad weather in the Mado waters.

Mado Shipwreck No. 5 also offers clues to shipbuilding techniques of the period.

An examination of the outermost structural components found that they had been treated through a process of smoking and charring with hot smoke to prevent the bottom of the ship from rotting.

Jin said Shipwreck No. 5 differed from No. 1 in both construction techniques and shape, noting that the latter was made of logs that had undergone little processing, while the former used thin planks that had been precisely shaped.

The institute also found traces that may belong to a sixth Goryeo-era vessel, designated Mado Shipwreck No. 6.

A preliminary survey of 10 sites focusing on underwater sediment layers uncovered more than 20 artifacts, including wooden tablets, celadon, a bronze spoon, a long-necked ceramic water bottle, bundles of rice and wooden cargo supports.

One wooden tablet says that a man named Mok Ryang, a local official known as a hojang in Saju, sent the cargo. Saju corresponds to present-day Sacheon, South Gyeongsang Province.

The institute said the area was home to Tongyangchang, one of 13 government grain depots that stored tax grain during the Goryeo period, adding that this is the first case of a ship believed to have departed from the Gyeongsang region.

All artifacts associated with Mado Shipwreck No. 6 are believed to date to the Goryeo period.

The institute plans to continue underwater surveys through this week and conduct excavations next year focusing on the discovery sites of Mado Shipwrecks Nos. 5 and 6.

The waters around Mado in Taean have long been known for their treacherous currents and were called "Nanhaengnyang," meaning a difficult passage.

Ships carrying grain collected as taxes from Chungcheong, Gyeongsang and Jeolla provinces had to pass through the route to reach Gaegyeong or Hanyang, the capital during the Joseon Dynasty. Despite the dangers, vessels continued to sail through the waters, where maritime accidents were frequent.

According to records in the Annals of the Joseon Dynasty, about 200 ships sank in the Taean area around Anheungnyang, also known as Nanhaengnyang, over roughly 60 years from 1392 to 1455.

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