Israeli authorities say they have recovered a papyrus document which appears to be nearly 2,000 years old.
The document measures 15cm by 15cm (6in by 6in), and contains 15 lines of ancient Hebrew script.
It appears to be a legal instruction, transferring a widow's property to her late husband's brother.
It was seized from two Palestinian men in a sting operation at a Jerusalem hotel, police said. The two could face several years in jail.
The Israel Antiquities Authority (IAA) said on Wednesday that the scroll was an "exceptional archeological document, of the like but a few exist," reported Israeli newspaper Haaretz.
It said similar scrolls had been sold worldwide for sums as high as $5-10m (£3.3-6.6m).
According to the Israel Antiquities Authority (IAA), the document is written in a style of ancient Hebrew primarily associated with the Dead Sea Scrolls.
These are scriptures and apocalyptic treatises thought to have been collected by an ascetic Jewish community which lived in the desert near the Dead Sea, and preserved by the dry climate.
But it remains unclear exactly where this document was obtained, said police and archaeologists.
Unusually, the first line of the document indicates a precise date, the IAA said - "Year 4 [AD] to the destruction of Israel", which could indicate either AD74, four years after Jerusalem's Second Temple was destroyed, or AD139, four years after the date of a Jewish revolt violently put down by Rome.
The document appears to concern the transfer of property belonging to a widow called Miriam.
The IAA's Amir Ganor cautioned that the document would have to undergo laboratory analysis to authenticate it.
Under Israeli law, all archaeological artefacts are state property
But he expressed excitement about the discovery, suggesting that the "very important" document could "shed light on how the people of the period managed their affairs and supplement our knowledge about their way of life".
The two suspects were reportedly apprehended while trying to sell the document, by police and Israeli intelligence officers who had planned the operation for weeks.
According to Israeli antiquities law all archaeological artefacts are state property.
The arrested men could be charged with illegally possessing and trafficking the artefacts, and could face years in jail if convicted.