I think about the Hyborian Age a lot. Maybe not quite as much as the Roman Empire, but more than 'now n’ then'.

I've been a student of Hyborian Age cartography since I was barely a teenager. The same goes for Hyborian Age lore, only that goes even further back. Here is something that I noticed quite few years ago, but have never commented on:

"In the north the Baltic Sea was formed, cutting Asgard into the peninsulas later known as Norway, Sweden and Denmark, and far to the south the Stygian continent was broken away from the rest of the world, on the line of cleavage formed by the river Nilus in its westward trend. Over Argos, western Koth and the western lands of Shem, washed the blue ocean men later called the Mediterranean. But where land sank elsewhere, a vast expanse west of Stygia rose out of the waves, forming the whole western half of the continent of Africa." — Robert E. Howard, “The Hyborian Age”

Did you catch that? What we now call 'Africa', Robert E. Howard (apparently) thought of as the "Stygian continent"--at least during the Hyborian Age. Now, it's basically impossible for said continent to have suddenly become 'Stygian' at that point in "The Hyborian Age" essay. The Stygians had already been cast down by the Vanir at that juncture in REH’s pseudo-history. We also have the fact that REH covered all that in this sentence: “a vast expanse west of Stygia rose out of the waves, forming the whole western half of the continent of Africa.”

Obviously, things went from the “continent of Stygia” to the “continent of Africa” in fairly short order.

It makes sense to speak of the “Stygian continent”. Stygia, over its extremely long history, had dominated the northern half of what we now call 'Africa'. If said ‘continent’ had any dominant culture to speak of, it was Stygian. For those who say that "half ain't enough", the same would apply to the 'Hyborian continent' to the north—maybe moreso. With this example from Howard, I would posit that the eastern half of Eurasia might have actually been called the 'Hyrkanian continent'.

If there was a "Stygian continent", then it also makes sense for there to have been another 'continent' to the east, with the Vilayet Sea providing a barrier and dividing line far exceeding anything now separating Europe and Asia.

“Hyrkanian continent” would make more sense, name-wise, than other examples. While there seems little doubt Iranistan, Afghulistan and Vendhya were all settled about three thousand years before Conan—as we see in “Black Colossus”—by ethnic Hyborians, it could be argued that they were ‘intruders’ to some extent. Meanwhile, the Kosalans—probably (partial) descendants from some of the earliest true humans to inhabit this eastern landmass—are simply too marginalized and obscure. “Lemurian” doesn’t work. They already have their (long-sunken) archipelago.

However, there are two major branches from the Lemurians who were enslaved for millennia by the ancestors of the Stygians. One branch, after the massive slave revolt by the Lemurians—”Far to the east, the Lemurians, levelled almost to a bestial plane themselves by the brutishness of their slavery, have risen and destroyed their masters. They are savages stalking among the ruins of a strange civilization”—became the civilized, sedentary peoples of Khitai. The other branch became the Hyrkanians and rode west, conquering and plundering as they went.

Those Hyrkanians established Turan and various khanates east of the Vilayet Sea. They are—by far—the most dynamic force within their landmass during the Hyborian Age. Just as medieval/Renaissance maps would show anything beyond the Caspian Sea as “Greater Tartary”, anything east of the Vilayet could be called "Greater Hyrkania" or the “Hyrkanian continent”—the concept of a ‘continent’ itself being of recent, Western origin. We have historical precedent for this and REH is very likely to have known it.

Where are the dividing lines between the "Hyborian", “Stygian" and "Hyrkanian" continents? Robert E. Howard provides numerous details and hints that point to Stygia (along with the Shemites) having long dominion over the Kharamun Desert. A north-south line running south from the Vilayet and along the eastern edge of the Kharamun seems about right. The northern edge of the Stygian continent would run east from the bend in the Styx until it hit the north-south line. Such a line could very well coincide with the situation--long, long ago--when the ragged ancestors of the Stygians emerged from the wastes of the blue East and found themselves within striking distance of their promised land beyond the Styx.

My speculations and conjectures have taken me far beyond Stygia and 'Africa', but that is how these things go. If this is such, then that must be...