Complex sentence: Beginning no later than the early fifth century, Christian writers came to equate Saracens with Arabs, which in turn linked Saracens with Ishmaelites (descendants of Abraham's older son Ishmael) in some strands of Jewish, Christian, and Islamic genealogical thinking.
Split into simpler sentences: Beginning no later than the early fifth century, Christian writers began to equate Saracens with Arabs. Saracens were associated with Ishmaelites (descendants of Abraham's older son Ishmael) in some strands of Jewish, Christian, and Islamic genealogical thinking.