In Winter Quarters, the protagonist Camul tells us in the Prologue that he eventually comes to live in a place called Margu.
Vicki C. did some sleuthing and found a Wikipedia link (as usual handle with care): Margu. The Greek name is Margiana, and Jona Lendering has an entry Margiana:
Margiana (Old Persian Marguš): oasis in the Karakum desert, modern Mary (or Merv) in the southeast of Turkmenistan.
Margiana was situated on the boards of the river Murghab; this river, which was called Margos by the ancient Greeks, has its sources in the mountains of Afghanistan and flows to the north, into the Karakum desert, where it divides into several branches that disappear in the desert sands. The fertile delta (satellite photo) was called Margiana and was already occupied by farmers in about 2200-1700 BCE; their Bronze Age culture is known as the "Bactria-Margiana Archaeological Complex".
[...] In 53 BCE, Antiochia in Margiana received new settlers: ten thousand
Roman soldiers, taken captive by the Parthians at Carrhae.
They must have found the conditions of their captivity easier than they
expected; a few years later, the Greek topographer Strabo
of Amasia praises Margiana as a country especially blessed by nature,
and he must have received this information from the captives. more
Camul describes the land as "A Sea of Grass," which one just might imagine, looking at the above satellite photo. Here is Strabo (Book II, Chapter 1.14)
14 Well, then, let us pass on to the country that rises opposite to the Cinnamon-producing Country and lies toward the East on the same parallel. This is the region about Taprobane. We have strong assurance that Taprobane is a large island in the open, which lies off India to the south. It stretches lengthwise in the direction of Ethiopia for more than five thousand stadia, as they say; and from it, they say, much ivory is brought to the markets of India, and also tortoise-shell and other merchandise. Now if we assign to this island a breadth that is proportional to its length, and if we add thereto the expanse of the sea between it and India, the sum would be a distance of not less than three thousand stadia — as much as the distance from the border of the inhabited world to Meroë — that is, if the capes of India are to rise opposite to Meroë; but it is more plausible to set down still more than three thousand stadia. So if you should add these three thousand stadia to the thirty thousand stadia which Deïmachus gives as the distance to the pass that leads over Bactriana and Sogdiana, then all these people would fall outside the inhabited world and the temperate zone. Who, pray, would venture to maintain this, when he hears of men of both ancient and modern times telling about the mild climate and the fertility, first of Northern India, and then of Hyrcania and Aria, and, next in order, of Margiana and Bactriana? For, although all these countries lies next to the northern side of the Taurus Range, and although Bactriana, at least, lies close to the pass that leads over to India, still they enjoy such a happy lot that they must be a very long way off from the uninhabitable part of the earth. In Hyrcania, at any rate, they say that the vine produces one metretes of wine, the fig-tree sixty medimni of figs, the wheat grows again from the waste seed of the stubble-field, bees have their hives in the trees, and honey drips from the leaves; and this is also true of Matiana, a province of Media, and of Sacasene and of Araxene, districts of Armenia. But in the case of the latter districts this is not equally amazing, if it be true that they lie further south than Hyrcania, and are superior to the rest of the country in mildness of climate; but in the case of Hyrcania it is more amazing. And in Margiana, they say, it is oftentimes found that the trunk of the grape-vine can be encircled only by the outstretched arms of two men, and that the cluster of grapes is two cubits long. And they say that Aria also is similar, but that it even excels in good vintage, since there, at all events, the wine actually keeps for three generations in unpitched casks; and that Bactriana, too, which lies on the border of Aria, produces everything except olive-oil.
Bactria on Wikipedia has maps, and lovely images from an earlier era. The above map is courtesy Jona Lendering. (click to enlarge)
Bactria-Margiana Archaeological Complex (or BMAC, also known as the Oxus civilization)