The stone, which measures a metre by a metre-and-a-half (three feet by five feet) and weighs a tonne, was found near the Damascus Gate entrance to Jerusalem's Old City, with Israel's Antiquity Authority (IAA) calling it "one of the most important Latin inscriptions" discovered in the Holy City.
The six lines in Latin, engraved in the hard white limestone, are a dedication from the Roman army honouring Emperor Hadrian, who visited the city in 130 AD and whose many building projects included the wall named after him in Britain to demarcate a border of the Roman empire.
The IAA said the stone may have originally been set into a gateway.
It was found on top of a deep cistern, with a semi-circle cut through the lower part of the inscription to allow access to the water.
"We have testimony in a new medium – stone – and a remnant of an original monument," said Rina Avner, who led the IAA excavation along with Roie Greenwald.
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The event mentioned in the inscription took place before the so-called Bar Kokhba revolt (132-136 AD) against the Roman empire, she told AFP.
She said historians remained divided over whether the revolt was a result of harsh measures taken against Jews by Hadrian, who rebuilt the city with pagan temples and named it Aelia Capitolina, or if the decrees were punishment for the rebellion.
The latest finding is proof of "public official Roman building in the city" of Jerusalem in that year, she said.
While the inscription did not change the way history would be written, it was "another significant piece of the puzzle we’ve been trying to solve for a while," Avner said.