Complex sentence: The stairs were built some time before the reign of Tiberius and were not mentioned by name in any ancient texts that predate his reign, their first use as a place of execution being associated with the paranoid excesses of his later reign.
Split into simpler sentences: The stairs were built some time before the reign of Tiberius and were not mentioned by name in any ancient texts that predate his reign. Their first use as a place of execution is thusly associated with the paranoid excesses of his later reign.