Ancient Miles was the largest mannish empire ever to rule the North. It's great extent and centuries-long endurance means that even today, ages and ages after its passing, the imperial shadow still colors the cultures, attitudes, and technologies of men from Ralashar to the Cloudhome Sea. The memory of imperial might has faded from the minds of most individuals but that does not prevent the shadow of the empire from reaching out and affecting them even in the most basic of their everyday lives.
The most obvious and widespread remnant of imperial control is the practice of burning the dead. Men the North over have taken up this imperial standard and cremation is the norm in any area that was once ruled by the empire (save for Teral where, for dark reasons to do with the Necromancer, corpses are buried). The ritual cremation of the dead is common practice as far east as Claulan and all the way west to the sea-side seat of Kjellos. The Skinchanger Kingdoms and the Twin Empires do not practice it, so one can see a dividing line where the northward expansion of the empire ceased simply by the inherited culture of the region.
The empire was not, however, monolithic over time. Thanks in part to a system of education based on the elvish tutor-system (known as the paidea), nobility across the empire shared a common culture. But those below noble status who were not educated in the classics rapidly diverged from the imperial "norm," creating a number of sub-cultures that were regionally varied and eventually giving birth to such dialects as Dorlish Varan, High Varan, North Varan, and West Varan, all of which can trace their descendance back to the original Old Imperial Varan of the Fifth Age.
The early empire was nothing like the late empire, however. By the late Fifth Age the empire was highly stratified and had produced an entire service class who's main goal was to work in the imperial bureaucracy. These new men (homines novi) where despised by the entrenched gentility for their interference in great affairs of state. It is partly this hatred that caused the empire to shake itself apart with the death of Emperor Malleus and most of his court and retinue at the Battle of Ogris.
What are those things that remained when the empire was gone? For one, the inn is a product of ancient imperial law establishing wayhouses for soldiers, messengers, and travelers along the great roads. The roads themselves are another example, for they have been regularly tended and repaired in many places by dwarven craftsmen descended from those who first taught the imperials the art.
Yet, we have seen a withering of the common inn in many parts to be replaced by the presence of noble manors -- the modern nobleman gets his news from travelers and as such is more than willing to put up merchants, jongleurs, and sellswords in exchange for tales of the wider world and little more. Only in the great urban centers (Bataille, Tourons, Noranor, Miles herself) have they managed to flourish and that mostly on the money taken from mercantile ventures who must rest their great caravans or crews between loading and selling.
One of the empire's most cherished traditions, that of the Great Schools, has vanished entirely. Whereas in the imperial era there were between four and eight Imperial Schools of Magic at any given time, today there are none. These organizations were cabals of powerful wizards who shared traditions as well as magical secrets. The powerful tekhne manuscripts are a product of the old Schools -- books that contain within them the magical force to rewrite the very reader, changing their physical makeup.
Kjellan scholars often lament the introduction of what they refer to as "barbarous" ways in the old Milean homeland. Thegnari custom and the appearance of a warrior-nobility have replaced the ancient gentility of old and no families can realistically trace their lineage back to one of the great founders of the glorious city. Those who hold titles and land in this modern age are not those who are "of good breeding" as it were but necessarily those who can, by force of arms, serve their new emperor best.
Yet this trend is hardly new, for immediately after the empire fell the philosopher-nobility (sometimes referred to as the nobility of leisure) fell with it. Even in Kjellos, no matter what they say, there is a great profusion of warrior-nobles supplemented by a very few who have been ennobled for their service to the crown.
However, I would classify nobility itself as an imperial notion. For the Thegnari never had such ideas, and the Llyrians and Llernean concept of nobility was far different -- fairly castelike, if the old records can be believed. In the imperial tradition nobility is something one possesses by breeding, intelligence, and erudition. While the criteria of what makes a man nobilis may have changed (mostly to loyalty, strength, and honor) the concept of an achievable trait has not.