An amateur diver found a 3-foot sword off the Israeli coast - and filmed his discovery. It dates back to the Crusades.

• A scuba diver found a 900-year-old sword and ancient anchors off Israel's Carmel coast last week.

• The iron sword is 3 feet long and weighs 11 pounds. It likely belonged to a knight from the Crusades.

• The diver was wearing a GoPro camera, and Israeli authorities released video of his discovery.

Shlomi Katzin didn't expect anything out-of-the-ordinary during his dive along Israel's Carmel coast.

The amateur scuba enthusiast was exploring the area's waters on October 9 when he came across a giant sword, covered in shells and marine life, 13 feet under the Mediterranean waves.

The weapon was more than 3 feet long, with a foot-wide hilt. Nearby, Katzin also found giant metal and stone anchors and bits of pottery nestled in a 1,000 square-foot patch of sandy bottom.

Fearing that shifting sands might bury the treasure, the diver carried his finds up to the surface and immediately contacted the Israel Antiquities Authority (IAA). Israel has a law dictating that any artifacts found in the country be handed over to the authorities.

The agency thinks that the sword, which is made of iron, dates back to the Crusades - religious wars between Christians and Muslims in the Middle East between the 11th and 13th centuries.

"The sword, which has been preserved in perfect condition, is a beautiful and rare find and evidently belonged to a Crusader knight," Nir Distelfeld, an inspector for the IAA's Robbery Prevention Unit, said in a press release on Monday. "It is exciting to encounter such a personal object, taking you 900 years back in time to a different era, with knights, armor, and swords."

During his dive, Katzin wore a GoPro camera, and so he was able to film his own discovery. The IAA shared some of that footage with Insider and posted the video on its Facebook page. In it, you can see Katzin pick up the sword off the seabed and uncover several anchors as nearby lionfish watch. His breathing punctuates discovery after discovery as he uses flippers to maneuver.

The agency awarded Katzin a certificate of appreciation for good citizenship for handing in the sword.

Storms, currents, and waves bury and unbury ancient treasures

Local archaeologists had already been monitoring the area where Katzin went diving, about 650 feet from shore, because that part of the Carmel coast offers a natural cove. Ships have moored since the Crusades, the IAA said, so it's a prime place to look for artifacts.

But fickle undercurrents and waves constantly bury and unbury ancient treasures like those Katzin found.

"Even the smallest storm moves the sand and reveals areas on the sea bed, meanwhile burying others," Kobi Sharvit, director of the IAA's marine archaeology unit, said in the release.

According to Sharvit, the anchors found near the sword could be far more ancient than the weapon - dating back to the Late Bronze Age, 4,000 years ago.

The layer of sand that hid the sword is likely the reason it's so well-preserved.

Being entombed under the seabed meant that the sword wasn't exposed to oxygen, Sharvit explained to CNN. That protected it from rust. Still, it was covered in shells and other bits of marine life - the weapon weighed at least 11 pounds when Katzin turned it in.

The sword itself, however, is likely only 4.4 pounds, Sharvit said.

A relic of the Crusades

The cove where Katzin found the weapon is a mile or so from what was once a Crusader fortress, Sharvit told CNN. That, coupled with the sword's large size and shape, is what led experts to conclude that it probably belonged a knight from the Crusades.

Between 1096 and 1291, the Roman Catholic Church and western European nations sent Christian armies to reclaim holy sites in cities like Jerusalem and Constantinople, which were under Muslim control. Some battles during the Third Crusade occurred near Israeli beaches, since England's Richard I traveled south along the Carmel coast toward Jaffa to fight Saladin, a Muslim sultan.

The sword is now being examined in the IAA's National Treasures Department. Once the weapon is sufficiently cleaned and studied, the agency said it would ensure the finding is displayed to the public.

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