Archaeologists of the Friedrich Schiller University Jena said a 16-by 24-inch inch marble plate that may have been a tomb slab bears a Hebrew inscription and has been dated to A.D. 390.
The earliest archaeological evidence of Jewish inhabitants in the region of modern-day Portugal had been a tomb slab with a Latin inscription and an image of a menorah from 482, a university release said Friday.
The earliest Hebrew inscriptions from the region known until now date from the sixth or seventh century, researchers said.
"We were actually hoping for a Latin inscription when we turned round the excavated tomb slab," researcher Henning Wabersich said.
The archaeologists said they were unsure which language they were looking at, as the inscription was not cut with particular care, but they eventually received help from Spain.
"Jordi Casanovas Miro from the Museu Nacional d'Art de Catalunya in Barcelona -- a well-known expert for Hebrew inscriptions on the Iberian Peninsula -- is sure that the Jewish name 'Yehiel' can be read, a name that is already mentioned in the Bible," Wabersich said.