NEW YORK (NYTIMES) - Mr Shlomi Katzin attached a GoPro camera to his forehead, slipped on his diving fins and jumped into the waters off the Carmel coast of Israel, eager to go exploring.

On the sandy floor of the Mediterranean Sea, he found a sword. Archaeologists would later determine that it was about 900 years old. It weighed 4 pounds, measured about 4 feet long and originated from the Third Crusade, experts said.

"Oh yes, he was surprised and happy," said Dr Jacob Sharvit, the director of the marine archaeology unit at the Israel Antiquities Authority.

Mr Katzin said he would give the sword to Dr Sharvit's agency, but he wanted just one thing: a photo with the shell-encrusted weapon.

The recent discovery was welcomed in a country that takes immense pride in its history and has a law requiring that any artifacts found must be returned to the nation.

The sword was among several artifacts discovered by Mr Katzin, who declined to be interviewed because he said he did not want the discovery to be about him. He also found stone anchors and pottery fragments that date back hundreds of years. But nothing was more impressive than the sword, which Dr Sharvit described as "extremely rare".

All of the items were found in the same 1,000-square-foot site. The authority has been aware of the location since June, after a storm shifted the sand. Still, finding artifacts remains elusive because of the movement of the sand.

"It's normal to find swords in bad condition, but this one was found under the water - and under the water, it was preserved in very good condition," Dr Sharvit said on Monday (Oct 18). "It's the first time that we found a beautiful sword like this."

The water off the Carmel coast remains the same temperature year-round, which helped preserve the iron in the sword. Because the iron was oxidised, shells and other marine organisms stuck onto it like glue, Dr Sharvit said. The discovery of ancient artifacts has increased as diving has grown in popularity in Israel, he said.

In the Second Crusade, the Muslim commanders defeated Western crusaders at Damascus, said Prof Jonathan Phillips who specialises in the history of the Crusades at Royal Holloway, University of London.

The sword would have been expensive to make at the time and viewed as a status symbol. It makes sense that it was found in the sea, Prof Phillips said, because many battles were waged near beaches, where Christian soldiers landed and were sometimes attacked by Muslim forces.

"It could have been from a knight who fell in the sea or lost it in a fight at sea," he said.

When Mr Katzin found it, he said he was afraid it would be stolen or buried beneath shifting sand, according to a statement from the authority.

The Israel Antiquities Authority's general director Eli Escosido praised Mr Katzin because "every ancient artifact that is found helps us piece together the historical puzzle of the Land of Israel". Mr Katzin was given a certificate of appreciation for good citizenship.

During the Third Crusade, King Philip Augustus of France, King Richard I (also known as Richard the Lionheart of England), and the holy Roman emperor, Frederick I (also known as Frederick Barbarossa), set out to retake Jerusalem. Saladin, the ruler of an area covering modern Egypt, Syria and Iraq, had conquered it in 1187, said Prof John Cotts, who specialises in medieval history at Whitman College in Walla Walla, Washington.

At the time, Pope Gregory VIII tried to inspire Western Christians through "great emotional language" to retake Jerusalem from Muslims, but ultimately the Muslim army maintained control of the city, Prof Cotts said.

"Traditionally, the definition of a knight is someone on horseback who engaged in mounted warfare," Prof Cotts said. It is possible that the sword belonged to one of them, and has survived for nine centuries, Dr Sharvit said.

After the sword is studied and cleaned, it will be placed in one of the country's museums, Dr Sharvit said. He would not disclose how much it could sell for, he said, because in his opinion, it was "priceless".

"Every artifact we find is always a really great feeling," he said. But this one "is very, very special".