Eutopia" by Poul Anderson and Eon by Greg Bear.
In Conquistador, SM Stirling turns this Alexandrian premise on its head. Alexander lived to seventy and bequeathed a vast, undivided empire that lasted for a hundred years but then fell apart in civil wars and barbarian invasions. Its twentieth century legacy is city-states, kingdoms and tribes with late medieval technology worshiping Zeus-Alexander and an undiscovered New World ripe for conquest from a timeline very similar to ours.
That is it for this month, folks. Posts will resume some time in July.