I took that information from a German-language website. It was illustrated by an early 11th century statement by the Bishop of Speyer, who prided himself to have turned Speyer "from a village to a city" by settling Jews. In the meantime, I have learnt from another website that said Bishop primarily advertised Speyer among Jews from nearby Mainz. Thus, aside from the Jewish community in Mainz being numerous enough to nourish other communities along the Rhine in the early 11th century, I currently can't contribute any further details on the sources and magnitude of Jewish migration from Italy to the Rhine.
I agree for the High Medieval period, from the 13th century onwards. For the early Medieval, I wouldn't be that sure:
Cologne had been one of the largest Roman cities north of the Alps, with an estimated population of 45-50 thousand during the second century AD (the city walls enclosed 120 hectares). There is some archaeological evidence of Jewish settlement commencing shortly after the Roman destruction of the Temple of Jerusalem. Ursurpator Postumus in 260 made Cologne the capital of his short-lived Gallic Empire that covered Iberia, Gaul, Britannia and Germania west of the Rhine. Roman civil wars, and several Frankish incursions, caused a population drop during the late 3rd to early 5th century to 15-20 thousand inhabitants, still a very sizeable city for the period. Cologne survived the migration period relatively unharmed - Attila, e.g., bypassed the city during his incursion into Gallia in 451. By the 6th century, the population still spoke Latin. A good part of the Roman infrastructure, including the water supply from the Eiffel mountains, was maintained and occasionally refurbished during the early middle ages. There is furthermore archaeological evidence of the co-existence of Germanic paganism with Christianity during the 6th century, which probably means that Jews as well didn't have much acceptance problems.
Cologne quickly became the capital of the Ripuarian Franks, initially subjugated to the Salingian Franks, but from the 7th century on the leading Frankish tribe. Most
Major Domi under the Merovingian kings resided in Cologne. It lost the function of capital in 751, when Pippin the Younger took over power from the Merovings, and relocated the capital to Aachen. Population during the early middle ages is assumed to have at least remained at around 15,000. By 1180 (extension of city walls to enclose 400 ha), Cologne is estimated to have had around 40,000 inhabitants, and may even have come close to 50,000 in the late 14th century. It was by far the largest high Medieval German city, and the fifth or sixth-largest in Western / Central Europe (after Paris, Milan, Prague and Florence; Brussels may have had a population equal to Cologne).
Mainz (Mogontiacum) may have been almost as populous as Cologne during its time as capital of
Germania Superioris and later
Germania Prima- the 4th century Roman city walls enclosed an area of 96 ha. There is archeological evidence of Jewish presence during Roman times, a 15th century document even claims that a Jewish community already existed during the 1st century BC, when Mogontiacum was still a Celtic town. The city may have suffered quite a bit during the migration period - the famous crossing of the Rhine in 406 AD occurred nearby, and Vandals devastated the town. Attila also passed through, and a few decades later Franks fought with the Alemanni over control of Mainz and the Upper Rhine. Nevertheless, from the 6th century on the city was rebuilt, partly following the original Roman layout, so destruction has most likely not been complete. Under the Carolingians, Mainz became an important political and religious centre; the Archbishop of Mainz held not only territorial authority over the town and the region, but also supervised most bishops in Southern and Eastern Germany (including, e.g., Prague), and the clergy at the royal court. The power culminated in the late 10th century when Archbishop Williges ruled the Frankish Empire on behalf of his godson, Emperor Otto III.
It is probably not a coincidence that during the same period Mainz' Jewish community became the largest and most influential within the Frankish realm. The first evidence of such a community is from the records of a late 9th century Synod in Mainz. The Mainz Yeshiva (Jewish Academy) founded by Gershorn ben Judaa became the intellectual centre of Central European Judaism over the next four centuries. Some sources (including the Wikipedia article below) speak of up to 6,000 members of the Jewish community in Mainz. Considering that the city as a whole is estimated to have had some 5-10 thousand inhabitants during the High Medieval, the figure seems exaggerated. However, some 20-25% Jewish share in the total population seems easily possible.
From the twelfth century on, nearby
Frankfurt/ Main started to politically and economically overshadow Mainz. Frankfurt's Jewish community grew correspondingly.
Strasbourg (Argentoratum) was only a medium-sized Roman provincial town. It was destroyed by the Allemans in 355-357, and again by Attila in 451, to be re-established by the Franks in 496. Initially rather small (only 1,500 inhabitants during the 8th century) it grew rapidly in the 11-12th century to around 10,000 inhabitants. A late 14th century extension of the city walls, which afterwards enclosed 200 ha, suggests further population growth to around 20,000.
I couldn't find sources on the establishment of the Jewish community in Strasbourg, but it most likely happened simultaneously with the general population expansion, i.e. sometimes in the late 10th century. In any case, before the Strasbourg Pogrom of 1349, 1,884 Jews lived in the city (half of which were killed during the pogrom). This would mean a Jewish population share of at least 10-15%.
Worms, (Borbetomagus) is another medium-sized Roman provincial town that suffered heavily from the Vandal's crossing of the Rhine. Claims are made for a Jewish community already existing there in the 5th century BC, but the first written evidence to such a community dates from the second half of the 10th century AD. Unlike Strasbourg, Worms was already an important Carolingian residence during the 9th and 10th century. At the onset of the Investiture Controversy, the citizens of Worms in 1073 expelled their local bishop (who had sided with the pope), and opened the city gates to Emperor Henry IV. Henry returned the favour by in 1074 granting the city a customs privilege, addressed to "Judai et coetieri" ("Jews and others"), which indicates that Jews were dominating the local economy, and probably also made up a substantial part of the city's population. The death toll during the First Crusade is estimated at some 800 Jews from Worms, which would be 10-15% of the city's estimated population of 5,000-8,000.
According to Wikipedia (first article from the list below), "about 12,000 Jews are said to have perished in the Rhenish cities alone between May and July 1096" (i.e. during the First Crusade). Adding up the city populations given above, and furthermore including Trier (5,000-10,000 inhabitants) yields a total population of at maximum 50,000 in the cities concerned (note that Jews in Speyer were spared, and there is also no mentioning of Jews from Bonn being prosecuted). This would mean that some 25% of the total city population were massacred, and imply an even higher share of Jews (some of which fled or converted) in the urban population. If the figure of 12,000 is correct, most of it should furthermore relate to Cologne (800 Jews killed in Worms, "a few hundred" in Mainz, etc.). That would mean that up to 50% of Cologne's population had been Jews before the First Crusade.
All in all, figures on the Jewish death toll during the First Crusade appear to be greatly exaggerated. I nevertheless think that Rhenish cities had a sizeable share, possibly 15-25%, of Jewish inhabitants. And, while the First Crusade undoubtedly damaged the Jewish communities, they remained strong enough to flourish for another 300 years in the region. Below is a map that shows all Jewish communities in the Rhineland during the early 14th century (black dots indicate Jewish cemeteries), which demonstrates that during the High Medieval Judaism expanded also to the countryside:
What does this mean in relation to the original question?
- The Jewish community in the Rhineland may already date back to early Roman times. Ashkenazi may have arrived directly from Judea, and survived the migration period relatively unharmed in Cologne, possibly also in Mainz and Worms. During early Roman, and especially early Frankish times, external social barriers to marrying non-Jews should have been relatively low, certainly not higher than in contemporary Italy.
- If the Jewish community does not date back to Roman times, it must have grown quickly from the early 10th century onwards. Possible migration sources include France (where the overall climate towards Jews appears to have been far less favourable during that period), Southern Italy (threatened by Arab invasions), and the Byzantine Empire. The latter deserves specific attention due to the marriage of Emperor Otto II with the Byzantian princess Theophanu. Theophanu ruled the empire together with the Archbishop of Mainz, Williges, from 985 to 994, until her son, Otto III, had become old enough to take over,
- It is not unlikely that a relevant part of locals converted to Judaism. Jews were outside of traditional tribal laws. This meant in particular that they were freed from armed service, and also from paying excises. They were furthermore not subjugated to traditional local courts (headed by Germanic counts or dukes), but had their legal matters directly settled by the royal court. Not too bad, especially if you are living close to the main royal palaces, i.e. in the Rhineland. [[In fact, a lot of the pogroms may be explained as either connected to anti-royal opposition, or as attempt to counteract a perceived "unfair" Jewish preference in economical matters; see the first Wikipedia article below. Don't get me wrong: Perceived "unfair competition" does not make discrimination and murder legitimate, neither in the 11th or 14th century, nor between 1933 and 1945!]
- Whatever was their origin, the urban Jewish population should have been sizeable (and wealthy / influential) enough to leave genetical traces in the non-Jewish population. Conversion is one issue here, faithfulness another (note that Imperial decrees allowed Jews to employ non-Jewish house servants).
http://en.wikipedia.org/wiki/Histor...ltural_and_religious_centre_of_European_Jewry
http://en.wikipedia.org/wiki/History_of_the_Jews_in_Cologne
http://en.wikipedia.org/wiki/Frankfurter_Judengasse
http://fr.wikipedia.org/wiki/Pogrom_de_Strasbourg[/U](in French - the article is much more detailed than the English version)