Photographs show different viewpoints, dates and conditions. They do not establish current access to a particular route. Every image is credited below.
Rome rarely presents one period in isolation. Streets lead between ancient structures, churches, palaces and living neighbourhoods, while the Vatican adds a distinct concentration of art and religious meaning. Rather than memorising a sequence of dates, notice where a later city reused an earlier space. A single well-chosen walk can connect more ideas than several hurried museum visits.
Give the Vatican and ancient Rome separate blocks of time. Major reservations work best as anchors around which the rest of a neighbourhood visit can breathe.