A 3,500-year-old tablet recounting the epic of Gilgamesh was returned to Iraq on Thursday after being stolen three decades ago and illegally imported to the US.
Iraqi Cultural Minister Hassan Nazim accepted the tablet at a ceremony in Washington.
"To me, it means restituting self-esteem and the confidence in Iraqi society," Mr Nazim said.
Despite its small size, the ancient artifact has immense cultural and historical value.
It contains portions of the Epic of Gilgamesh, considered one of the oldest works of literature in human history. It tells the story of a powerful Mesopotamian king on a quest for immortality.
"It's a story that has influenced all the great monotheistic religions, leaving traces also on the Iliad and the Odyssey," said Unesco Director General Audrey Azoulay, who called the tale a treasure for "our common humanity".
Ms Azoulay said the stone's return to its rightful home was "a major victory for the international community over those who mutilate heritage".
"Its repatriation itself is a tale of epic proportions," said US assistant attorney general Kenneth Polite.
The clay tablet, carved with cuneiform characters, is believed to have been stolen from an Iraqi museum in 1991, about the time of the First Gulf War.
It reappeared in Britain in 2001, Mr Polite said.
An American art dealer bought it from a London-based Jordanian family in 2003, before sending the piece to the US without declaring its true nature to Customs.
It was then sold to antique dealers in 2007 for $50,000 under a false certificate of origin.
The tablet was sold again in 2014 for $1.67 million to the owners of craft chain Hobby Lobby, the Green family, fundamentalist Christians who wanted to display it at their Museum of the Bible in Washington.
A museum curator became concerned about the tablet's origins in 2017, feeling that its documentation was incomplete. It was finally seized in 2019.
Iraq's Ministry of Culture called on other organisations to scrutinise artifacts of dubious provenance to try to uncover other missing treasures of antiquity.
"We invite all universities, museums, institutes [and] antiquities collectors to confront the illicit trafficking of artifacts to show more care and interest in restituting those which have been trafficked to the country of origin," the ministry said.
About 17,000 antique artifacts were already returned to Iraq from the US in July. The pieces mostly dated from the Sumerian period, about 4,000 years ago, one of the oldest civilisations in Mesopotamia.
Iraq has had its historical artifacts looted for decades, including since the US invasion in 2003.