It was called etrog and was used by Jews during the week-long festival of Sukkot as one of four species (lulav - a closed leaf of the date palm, hadass - a branch of myrtle - aravah - a leafy branch of willow and etrog).
Many archaeological sites from that era feature an image of the etrog (including mosaics in Beth Alpha, Maon and Hamat Tiberias synagogues), depicted alongside other important religious symbols.
The Book of Leviticus mentions the citron as "the fruit of a beautiful tree."
In 2012, citron pollen from the 2nd century B.C. was discovered in Israel in excavations at the Ramat Rachel site.
