How much of our Earth do you think is still around by the BT setting? By that I mean, we know the Great Pyramids at Giza are still standing they were seen in on the cover of a source book. What about the Great Wall of China? How did the monuments in Washington DC fare? Do you think Comstar/Word of Blake held ceremonies at Stonehenge? Would anyone wonder (or know) who the faces on Mount Rushmore are supposed to be? Is the Hoover Dam still supplying power to a futuristic Las Vegas? Does the Pope still lead the Catholic Church from the Vatican? Is the Eiffel Tower still in Paris? Does the Republic of the Sphere draw inspiration from preserved documents like The US Constitution, the UN (or Western Alliance) Charter, or Magna Carta? Did someone find a way to preserve the Leaning Tower of Pisa, or did it finally fall over? Do Holovid Stars still put their names in the Hollywood Walk of Fame? Those kinds of things.
Another question. Prior to the Fortress, how likely would it be for someone to visit Earth and see such sites? Not warriors or political leaders, but more common people like historians, wealthy merchants on vacation, pilgrims to Mecca (if BT Islam still requires that), or otherwise curious people with the means and wish to visit mankind’s cradle.