By the time Emperor Constantine I had founded a new capital of the Eastern Roman Empire at Byzantium (later Constantinople) in 324 CE (Common Era, equivalent to AD), Jews were widespread throughout the Roman Empire. Christianity was adopted as the official religion of the empire. Jewish communities across Europe and North Africa fell victim to religious intolerance. Jerusalem, the former Jewish capital, became a Christian city. In 380, Emperor Theodosius I issued a set of decrees directed against Jews: they were forbidden to own slaves, to build new synagogues, to hold public office, or to marry non-Jews. Later Byzantine emperors, including Justinian, further restricted the civil rights of Jews.

Golden Age in Spain

The Arab Empire, ruled by the Umayyad dynasty, conquered Spain in 711, beginning a long period of Muslim rule throughout much of the Iberian Peninsula. It also ushered in a Golden Age for the Jews who lived there already, or who migrated there from North Africa. During that time, Jewish religious, cultural and economic life prospered.

​​​​​​​However, the fortunes of the Jews all over the Arab Empire started to change in the 11th century. Muslims in Spain carried out pogroms (anti-Jewish violence) in Cordoba in 1011 and in Granada in 1066. Elsewhere, synagogues were destroyed and some Jews were forced to convert to Islam or face death.

The Arab Empire came under attack when the Crusaders fought to reclaim Jerusalem for Christianity. In 1099, Jews fought alongside the Arabs to defend the city. When it fell, the Crusaders rounded up around 6000 Jews in a synagogue and set it on fire. In Haifa, the Jews almost single-handedly defended the town against the Crusaders, holding out for a month.

​​​​​​​The Crusaders ruled the Levant (the area of modern Israel, Jordan, Lebanon and Syria), losing and recapturing it over a period of almost 200 years. During this time, the Jewish population were banned once more from Jerusalem and prohibited from owning land.

Medieval Europe

Jewish populations existed all over Europe, especially in the area of the former Roman Empire, since the first century AD. Early medieval society was tolerant towards Jews and their religion. Between 800 and 1100, some 1.5 million Jews lived in Europe. When the Church forbade Christians to lend money for interest, some Jews became moneylenders and bankers—and received protection from kings, princes and bishops.

From the 1100s onwards, the vast majority of Jewish people in Christian Europe became the subject of anti-Jewish preaching and suffered persecution. Some Jews were falsely accused of the murder of Christian children in order to use their blood as part of their religious rituals (“blood libels”). Others suffered from appalling massacres. Many were forced to convert to Christianity or be expelled. The Crusaders destroyed flourishing Jewish communities in Germany and France as they made their way to the Holy Land.