Aquilonian are related to the Zingarans, but the mixed racial heritage of these coastal peoples led discount them as Hyborians. The Zingarans are darker skinned than their Hyborian cousins and exotic in their habits. But this description also fits the people of Zamora, the two kingdoms and their populations are not related.
Aquilonia would emerge as the most powerful of the Hyborian kingdoms. The Hyborian culture of the time was described as dynamic, and its civilizing influence was felt by most of their barbarian neighbors. The Hyborians of the time had a mixed heritage and no longer closely resembled their ancestors, but this mixed heritage hadn't weakened them in any way. Slavery was widespread in the Hyborian world, creating the unintended side-effect of slaves mating with their masters. This produced bloodlines of mixed heritage in most kingdoms of the time, Hyborian or not.
Aquilonia itself contains at least three provinces with distinct cultural and hereditary differences from other Aquilonians.
The province of Gunderland to the north of the country doesn't contain slaves. The people of this province have undergone less interbreeding with other races than any other Hyborians of the time. They resembled the ancient Hyborians more closely than any of the others, remaining tawny-haired and gray-eyed.
The Bossonian Marches extended from the northern border of Zingara, throughout the Pictish border, to the south of Cimmeria, and the east of the Border Kingdoms. The Bossonians descended from a formerly independent race which was among the first to fall to the Hyborians. By this time, they possessed some Hyborian blood, but were distinctly different in appearance. They were people of average height and skin pigmentation, with either gray or brown eyes, and with mesocephalic skulls.
Their position at the borders of civilization with the barbarians never allows them to advance to the cultural height of other Hyborians. The Bossonians mostly are farmers settled in fortified villages, and their main concern is the protection of their land from barbarian raids. In effect, this also protects Aquilonia and the Hyborians from facing invasions by Picts or Cimmerians. Centuries of barbarian wars led to the Bossonians being particularly stubborn combatants, and their defense techniques were impenetrable by the direct charges favored by barbarian military commanders.
To the south, the province of Poitain had borders with Zingara. The relatively peaceful relations between the two civilized Kingdoms allows for people and goods to constantly flow through the borders. Interbreeding with the Zingarans caused the citizens of Poitain to be predominantly dark-haired and brown-eyed.
The Pictish Wilderness and Zingara borders Aquilonia to the west. At the time of Conan, the Picts are more or less stagnant culturally and have not significantly advanced in millennia. Aquilonians and the Picts often engaged in border wars, where Pictish tribes attempt raids and Aquilonian armies and colonists attempt to expand their kingdom towards the west, but met with fierce resistance in either case, the profits of these campaigns were meager and costly in terms of casualties.
The Zingarans are an emerging naval power with a focus on having competitive military and merchant fleets with Argos and Stygia for dominance of the Western Sea. The maps of the Hyborian world depict a small territory where the southern borders of Aquilonia with Zingara and Ophir are at a very small distance from the northern borders of Argos with both states.
The southern borders of Aquilonia are with both Zingara and Ophir. Ophir is a gold-mining region. By the time of Conan, Aquilonia and Ophir were allies.
The eastern borders of Aquilonia are with Nemedia, the second most powerful of the Hyborian kingdoms and likely a bit more advanced culturally. The two main competitors for dominance of the Hyborian world will often engage in wars, though neither manages to gain dominance over the other. Nemedia is frequently mentioned as the main source of Hyborian philosophy and Nemedian priests of Mithra are spread across the Hyborian world in their efforts to convert others to their religion.
The northeastern borders of Aquilonia with the Border Kingdoms would serve to prevent Aquilonia from having direct borders with Hyperborea and an even more extensive border with Cimmeria. The extent of Aquilonian influence over this area is uncertain, though pastiche writers have depicted Aquilonian colonial efforts.
The northern borders of Aquilonia are with Cimmeria. The Cimmerians are descendants of the people of Atlantis who managed to survive the cataclysm. They are still barbarians, but have avoided the cultural stagnation of the Picts. The nine kingdoms states that they maintain contact with their northern neighbors in Vanaheim and Asgard, their eastern neighbors in Hyperborea, their southeast neighbors in the Border Kingdoms, their southern neighbors in Aquilonia, and their western neighbors in the Pictish Wilderness. Through these contacts, they become increasingly familiar with the advances of other people and undergo a gradual cultural development themselves.
The Cimmerians are consistent of various warlike tribes. They engage in war with each other when not actively and stubbornly defending their territory from the raids and military invasions of their neighbors. They are fiercely independent and resist all attempts at conquest. They perform raids to the realms of others but are either unable or uninterested in expanding their territories. Aquilonia manages to successfully defend itself from the raids and their efforts to expand in Cimmerian grounds meet with fierce opposition. These borders remain surprisingly stable after centuries of warfare.
A cross between the Roman Empire and Carolingian Empire. The name is borrowed from Aquilonia, a city of Southern Italy, between modern Venosa and Benevento; it is also an ancient name of Quimper and resembles that of Aquitaine, a French region ruled by England for a long portion of the Middle Ages. The name is derived from Latin aquilo(n–), "north wind".
- Hyborian Age#Aquilonia on Wikipedia