(Found) Personal portal to alternate history world

[TomMazanec]

21st century novel. Second tier author (not Asimov or Clarke, but well known).
PoD was Alexander the Great living to old age, more successful empire that invents printing press and preserves Classical Greek writings.
Hero sets up own colony in America (which had not been discovered yet by Europeans/Asians).
At end "lose" portal and they open new one to ATL where American megafauna still thrive.

 

[tachyon]

Conquistador by SM Stirling

(google search terms: "alexander the great" alternate history "novel" "america")

 

[TomMazanec]

That’s it.
Found

 

[Jubal_Harshaw]

21st century novel. Second tier author (not Asimov or Clarke, but well known).
PoD was Alexander the Great living to old age, more successful empire that invents printing press and preserves Classical Greek writings.
Hero sets up own colony in America (which had not been discovered yet by Europeans/Asians).
At end "lose" portal and they open new one to ATL where American megafauna still thrive.

Definitely Conquistador by Stirling.

 

[Jubal_Harshaw]

PoD was Alexander the Great living to old age, more successful empire that invents printing press and preserves Classical Greek writings.
Hero sets up own colony in America (which had not been discovered yet by Europeans/Asians).
At end "lose" portal and they open new one to ATL where American megafauna still thrive.

Just a clarification. The OTL was actually OUR timeline (or something very like it), and the portal was to the Alexandrian timeline that the OP describes (the ATL). For a variety of reasons, the civilizations of the ATL do not ever find/explore the Western Hemisphere, so those two continents are basically pristine.

It is one portal between only those two worlds. The transfer device is damaged/destroyed, and when repaired/replaced, it opens a new portal, but to a DIFFERENT alternate world ... this one with the megafauna. Seeing a Smilodon on the other side of the portal is the last scene of the book, so we do not KNOW anything about the remainder of that world.

I always wished that Stirling had returned to this concept, but he has said multiple times that its lack of monetary success means that he will never do so.