The diver, Shlomi Katzin, discovered the metre-long blade on the seabed along the Carmel coast, the country’s Antiquities Authority has announced. Shlomi Katzin noticed several remains, including pottery fragments, stone and metal anchors, before he noticed the blade itself.
He was diving about 200 metres out to sea when he made the discovery last weekend.
Mr Katzin brought the sword up to the surface, as he was worried the precious object may become covered by sand.
The Israel Antiques Authority (IAA), who Mr Katzin alerted once he was back on dry land, confirmed the sword likely belonged to a Crusader knight.
Nir Distelfeld, IAA inspector, said: “The sword, which has been preserved in perfect condition, is a beautiful and rare find and evidently belonged to a Crusader knight.
“It was found encrusted with marine organisms but is apparently made of iron.
“It is exciting to encounter such a personal object, taking you 900 years back in time to a different era, with knights, armour and swords.”
Kobi Sharvit, head of the authority’s marine archaeology unit, said: “The shape and, of course, the location leave no doubt that it is of Crusader provenance.”
The sword has a metre-long blade and 30-centimetre hilt.
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Mr Katzin said he found the sword buried in shallow water, at a depth of about four or five metres, in an area regularly frequented by scuba divers.
Shifting sands at the bottom of the sea are believed to have uncovered the object, which lay buried for hundreds of years.
The Crusades were a series of religious wars between Christians and Muslims, which started primarily to secure control of holy sites considered sacred by both groups.
Eight major Crusade expeditions occurred between 1096 and 1291.
Mr Sharvit said that discoveries like this are becoming increasingly common.
He said: “The discovery of ancient finds by swimmers and leisure divers is a growing phenomenon in recent years, with the increasing popularity of these sports.
“It is therefore vitally important to report any such finds and we always try to document them in situ, in order to retrieve as much archaeological data as possible.”
Mr Katzin received a certificate of appreciation for good citizenship for his discovery.