So eeeep gave some good examples but they all tend toward the higher end strategic/warfare/state based side of things.

I'm going to talk a bit about raids in the context of "raiders" who may or may not be attached to armies and whose strategic goals are often a lot more practical and short-term. I will also be confining myself to examples from the early medieval period, say 700-900 or so.

Fear and damage were both key parts to raids, yes. The Carolingians spent a lot of time marching armies into areas like Saxony, Brittany, Central Europe, etc. largely in order to cow populations and put down resistance. Burning villages and settlements was fairly typical of these military engagements, in fact way more typical than fighting pitched battles. These raids certainly struck fear and worked to cement control over an area, and they also damaged their enemy. But, perhaps most importantly, raiding brought wealth and prestige to the raiders.

Raiding allowed for the seizure of goods, perhaps most importantly in this period, the taking of slaves. Seizing slaves provided a major source of income to raiders and it is telling, for instance, that the very root for the word Slave comes from the ethnic name Slav, as they were the constant target of raids from both Scandinavian (i.e. Viking) and western (Carolingian and Ottonian, etc.) peoples. Raiding was the primary way to make money for most people in this period. Carolingians went on campaign raiding and destroying their enemies settlements and then distributed that acquired wealth throughout society in the form of gifts and commodities. Likewise, Vikings built up their prestige at home by raiding and destroying Frankish and Anglo-Saxon towns and then using the wealth gained to earn the support of more men or to settle down on a farm.

As to why fire, a few theories have been put forth. It may have just been a standard part of how you attack. It may have been used as a distraction or as a fear tactic, a way to decrease your danger and increase theirs. It may also often have been an accident. Early medieval architecture was not, let say, robust. We hear about fires in lots of non-combat contexts so it is not surprising that structures made of wood and straw have a tendency to combust during conflicts.

A final note though, about "destruction." We have to be very careful about trusting our sources too far when it comes to the destruction of a village. Very often Latin sources have a tendency to over-state just exactly how "destroyed" a place was. We hear destroyed and think, ok, that place is gone. But really we have lots of examples of places that are said to be destroyed which ether appear again in the records or appear in the archaeological records with no sign of fire or destruction layers.

Dorestad, the major trading port of the Franks, located about 20 miles (32km) up river on the Rhine from Utrecht, is stated to have been burned and destroyed in 834, 835, 836, and 837. Then again throughout the ninth century until the late 870s. Clearly, if Vikings can "burn" and "destroy" the town and carry off the population every year for four years running, we have to ask just how destroyed it really was each time.

And in fact the old theory that Dorestad was basically obliterated by constant Viking activity has now given way to a belief that, in fact, it was shifting river beds which did in the trading port. A much more mundane end.

I hope that gives you some ideas about the nature of raiding and also about the problem of "destruction" in the early medieval period.

Some things to read.

• First and foremost Timothy Reuter's article "Plunder and Tribute in the Carolingian Empire" in Transactions of the Royal Historical Society 35, 1985 75-94.

• Also take a look at Guy Halsall's Warfare and society in the barbarian West