The community, shrunk by emigration to around 300-400 families from a peak population of over 10,000 in the middle of the last century, is based in the even more ancient city of Derbent on the western shore of the Caspian Sea, on an old north-south trade route skirting the Caucasus mountains.
Dagestan became part of the Russian empire in 1813, when Tsarist forces prised it away from Persia.
Known locally as "Mountain Jews", they speak a dialect of the Farsi or Persian language spoken in Iran to the south.
This fact led Soviet authorities to designate their "nationality" - or ethnicity - in passports as "Tat", an umbrella term for Persian-speaking peoples who lived in many parts of the northern slopes of the Caucasus.
Derbent, a city of 120,000, is their religious and cultural centre, but has only one synagogue.
Some scholars believe that the first Mountain Jews, like members of many other Jewish communities, started to emigrate to a prospective homeland in what was then Ottoman-ruled Palestine as early as the 19th century.
Since the easing of emigration restrictions in the later years of the Soviet Union, the bulk of Dagestan's Jews have emigrated to Israel.
Rabbi Ovadia Isakov, the best-known contemporary Mountain Jewish rabbi, told Russian media that 300-400 families remained in Derbent.
Isakov was shot in the chest in 2013 as he got out of his car to enter his home. After lengthy treatment and rehabilitation in Israel, he returned to Russia.
Shneor Segal, the chief Ashkenazi rabbi of Azerbaijan, which borders Dagestan to the south, said the latest events were a terrible reminder that "even in our region, the Caucasus, where Jews have already been all but decimated, anti-Semites will use any excuse ... to terrorise the dwindling numbers of us that still remain".
(Reporting by Filipp Lebedev; Editing by Kevin Liffey and Grant McCool)
