In ancient times, the word corresponding with "apple" actually referred to quince. (Modern large edible dessert-quality apples were yet to exist in Europe at that time)
So "Persian Apple" would have actually been a very apt description of a citron at that time.
Both fruits are yellow, hard, and very fragrant. Citrons actually have a little bit of a substance called ionones in their fragrance, which smell like violet flowers. The fragrance of quince includes this substance as well.
Both citron and quince are high in pectin, and so there are some similarities for culinary uses.
Citron probably came from the Northeastern region of India, diseminated over time across India and into the Persian Empire (typically as an exotic luxury item in the gardens of the wealthy), and then was taken by the Jews to Israel.
It wouldn't be until around 1000 AD that the next citrus variety arrived in Europe, the sour orange, and then another 300 years after that until the sweet orange arrived (though it would take another 200 years or so for it to become popular and spread).
Topic: The earliest evidence for citrus in Egypt. (Read 876 times)