Complex sentence: At some point following the Roman exile of the Jews from the Land of Israel, the actual identity of the source of the dye was lost, and during a period of over 1,300 years, Jews have only worn plain white tassles ("tzitzit").
Split into simpler sentences: At some point following the Roman exile of the Jews from the Land of Israel, the actual identity of the source of the dye was lost. Since that time, a period spanning over 1,300 years, Jews have only worn plain white tassles ("tzitzit").