@djur 13d
I don't see any viable way for Julius Caesar to succeed in Parthia. Compared to the Gauls, Parthia was far more politically cohesive, had better trained and equipped soldiers, and presented more logistical difficulties (Antony benefited a lot from having Cleopatra's support and still failed). Fighting a long and grueling war like that so far away from Rome would have meant leaving his domestic political situation in the hands of his allies -- and he didn't really have anybody capable he could trust to do that.
@chewz 12d
For me the person that had changed the fate of Europe is Quintus Caecilius Metellus Celer. Never heard of him?

Well Julius Cesar was supposed to receive command of Cisalpine Gaul and Illyricum. And his plan for winning glory (and money) was provoking a war and conquering in North East direction - Balkans and perhaps with his usual impetus toward Central Europe, perhaps as far as today's Ukraine.

But a person that have been nominated for Transalpine Gaul command Quintus Caecilius Metellus Celer had died unexpectedly and his imperium have been passed to Julius Cesar.

Now imagine that Julius Cesar and his legions had conquered Central and Eastern Europe while Western Europe had been left alone. And Augustus and further Cesars will continue in this direction.

@Simon_O_Rourke 12d
Caesar wanted to do a lap around the Black Sea after defeating the Parthians and work his way home through what was then Sythia.

Depending on how far they got, and there's more than a good chance that the Parthians may have destroyed any army sent against them. If not, then the Romans would have had to face the steppe horse archers a few hundred years earlier than otherwise. And that would never be easy.

@andrepd 13d
Re: Rome and Han China. This channel is great, and they have a video about the first-hand accounts of meetings between the East and the West https://www.youtube.com/watch?v=CO3senO4JZ0
@throwaway6734 12d
In this alternate timeline would Augustus still take over?

Without Augustus as the first emperor who knows if Rome would have lasted nearly as long as it did

@pyuser583 13d
His plan was to recreate Alexander’s invasion of the Indus.

He would have failed.