Hebrew peoples who fled Roman Christian persecution westward, or who were simply living in Hispania when it was conquered by the Visigoths, found themselves in the Visigothic Kingdom on the Iberian Peninsula. Today we call it mainly Spain. The Visigoths were Germanic Christians and they followed Arianism, rather than Trinitarianism. They considered Jesus to be the Son of God, holy and divine, necessary for Christian atonement, but not himself a deity. Trinitarian belief is founded on the proposition that God the Father, Jesus the Son, and the Holy Spirit make up a triune three-in-one God: each a deity, and all the same deity.
The First Council of Nicea Constantine presided over in 325 CE had established trinitarianism as the official faith of the Roman Empire, with death by burning as the punishment for anyone who kept writings of the heretic Arius after the Council. But Arianism didn’t die, it just spread north into the Balkans and the Germanic territories. By the time the Visigoths established their kingdom in the Iberian Peninsula, they’d been practicing a monotheistic Christianity for more than a century.
In previous conquered territory of Gaul (western France) they had tried simply tolerating the religious differences between them and their Catholic peasants, but that hadn’t gone very well. They’d also tried slaughtering clergy, burning churches, and forcibly converting trinitarians to arianism, without much success there either. In Visigothic Spain they decided to try something entirely new. They would convert to Catholicism themselves to ease relations with their conquered peoples.
Life in the peninsula hadn’t been too bad for Jews up until this point. They had integrated into all levels of society, with most as farmers and herders, but some as merchants and textile makers, and others in the capital as scholars, rabbis, and bankers. There are even records of gentile farmers paying rabbis to come bless their fields. Catholic clergy hated Jewish people, but that antisemitism was to be expected. During the long war years when Spain was a battleground, Rome did not enforce anti Jewish laws in the region.
As soon as the Visigoths won the war and declared theirs a new Catholic country in 586 CE, the first King established a series of anti Jewish laws. Jews were forbidden from offending Christianity in word or deed, from testifying against a Christian in court, from trying to flee a baptism by leaving the country. Jews were not allowed to circumcise their children, keep the Sabbath, observe Passover or high holy days, follow dietary Kosher laws, or celebrate Jewish marriages.The penalty for breaking these laws was death by stoning or burning. Conversely, any Jewish slave who converted to Christianity would be instantly granted their freedom.