It is not known from whence the Jewish community of sixth century Ravenna came from but their closeness to the Ostrogothic elite suggests that they migrated with the Ostrogoths from their previous settlement around the mouth of the Danube on the Black Sea. It is not known if the Danubian homeland of the Ostrogoths had a significant Jewish population but another Gothic settlement further east on the Black Sea, the Crimean Bosporus, had an old Jewish community which came under Gothic rule in about 362. (see Gibson, E. Leigh "The Jewish Manumission Inscriptions of the Bosporus Kingdom" Tubingen, Germany, Mohr Siebeck, 1999 for Jews on the Crimean Bosporus and Alexander Alexanderovich Vasiliev "The Goths in Crimea" Cambridge, Mass., Medieval Academy of America, 1936) for Goths in Crimea).
To flesh out this hypothetical reconstruction; the Ashkenazim began as Jews of the Crimean Bosporus who allied themselves with the Goths who got control of the Bosporus in about 262 CE. These Gothicized Jews joined the Ostrogoths of the lower Danube on their migration to Italy under the leadership of Theodoric the Great in 493. They settled in northern Italy, particularly in Ravenna and remained in northern Italy after the Lombards, a West Germanic people, conquered Italy in 568.
Jewish life in northern Italy is sparsely documented but by about 800 Jews are reported at least as traders to the north of the Alps in Regensburg under the rule of Charlemagne. After the death of Charlemagne in 841, the German lands did not thrive. An economic revival began under the Saxon Empire between 919 and 1024 associated with the rise of eastern German cities like Erfurt, Merseburg, Halle and Magdeburg, all of which are thought to have had significant Jewish populations. This period was followed by that of the Salian Empire from 1024-1125 when Jews, some of whom moved from northern France, settled in Speyer, Worms and Mainz (SHUM).