Complex sentence: On the Quirinal Hill is where Constantine ordered the erection of the last "thermae" of imperial Rome, though now lost, having been incorporated into Renaissance Rome, with only some drawings from the 16th century remaining.
Split into simpler sentences: On the Quirinal Hill is where Constantine ordered the erection of his baths, the last "thermae" complex of imperial Rome. These are now lost, having been incorporated into Renaissance Rome, with only some drawings from the 16th century remaining.