Complex sentence: The site was significant in Rome's sacred history: two shrines attested at the later Circus could predate its formal development, and probably determined the semicircular, southeastern turn of the track, opposite the starting end.
Split into simpler sentences: The site was significant in Rome's sacred history: two shrines attested at the later Circus could predate its formal development. Both were sited at what became the semicircular, southeastern turn of the track, opposite the starting end.