In 1516, some 900 Jews (rising to a peak of nearly 5,000 by the mid-17th century) were confined to what was then a remote and isolated island.
The Jews forbidden to leave the island, and those who attempted to were severely tortured as punishment. 
mnli hypothesis: The Jews forbidden to leave the island, and those who attempted to were severely tortured as punishment.  premise: In 1516, some 900 Jews (rising to a peak of nearly 5,000 by the mid-17th century) were confined to what was then a remote and isolated island.