Frisians! I will answer these in order, but first off, some basic background.

The Frisians were a Germanic barbarian group, probably originally from Scandinavia or the Baltic regions who migrated into the area that came to be known as Frisia (and which corresponds roughly with the modern Netherlands) during the end of the Roman Empire. They are quite closely related to the Saxons both the "Old Saxons" (i.e. the Saxons who remained in Germany) and to the Saxons who migrated to Britain. During the late antique period and the Early Middle Ages (say roughly 5th to 7th century) they were active as pirates, but also as traders which makes sense given that there lands were coastal and in fact were far more suited to maritime activity than to agriculture.

By the 8th century the Frisians had begun to coalesce into what can be regarded as a "kingdom," and had come into active contact and contention with the Merovingians and the Pippinid mayors (the pre-Carolingians).

Under Charles Martel, Frisia was actually conquered by the Franks and integrated over time into Francia. By Louis the Pious time (814-840) Frisia was fully integrated into the Carolingian empire. Frisians fought in the Carolingian armies, served as traders throughout the empire and beyond, intermarried with other important families etc.

In fact, they became known as the most important traders in the early Middle Ages, in large part because Dorestad, the most important emporia (market town) in the period was in Frisia. In many sources the word Frisian became synonymous for "merchant."

OK, with all that said, onwards to your questions.

1. So there is some confusion here in terms of time and activity. The "Viking Age" typically dates to c.800 to c.1050. By 800 Frisians were not particularly known for their piratical activities. Rather, as I stated above, they were known for their trading activities. Frisians were incredibly active throughout the North Sea. They settled along the coasts well into Scandinavia, note, for instance, the so-called Frisian Archipelago along the western coast of Denmark. They also created colonies as far as Sweden, having an active presence at all of the major Scandinavia trade ports (and some argue that they were instrumental in their emergence). They carried trade goods such as pottery, wine, glass to Scandinavia and brought home furs, amber and other goods. So they were very active, but not as pirates (though of course we can't rule out some piratical activities . . .)

2. See question one. In fact, during the Viking Age it is, unsurprisingly, the Vikings who are the major pirates wrecking havoc across the North Sea. The Frisans had been famous for their piratical behavior long before during the chaotic period of the migrations and early Barbarian kingdoms but having been integrated into a stable "state" this activity had dwindled.

3. This is very hard to answer since the people in question were all pre-literate at this point so we have no records. That being said, they were probably seen as familiar and perhaps even as "related." We know that Frisian elites held land across the Rhine in Saxony, even before the "conquest" by Charlemagne, and vice-versa. The languages must have been largely intelligable both in Saxony and in Scandinavia. The fact that Frisians served as the major "go-betweens" between Scandinavia and the Continent also indicates familiarity and "closeness." Of course, the fact that the Frisians were the major handlers of wealth also made them attractive targets for Viking activity. It is no wonder that the first major Viking attacks on the Frankish empire were focused on the Frisian trading port of Dorestad.

4. Not really, although they certainly were not the easiest to Christianize. We have quite a bit of literature on the on-going attempts to convert Frisians and their resistance prior to the conquest by Charles Martel, but by the mid 8th century they had been fully converted (as much as anyone was in this period). Dorestad had several churches and Utrecht, up the Rhine river was the seat of a major bishop and monastery. They did, however, retain a unique identity. For one thing they had their own law code, first set down by Charlemagne. They also were clearly regarded as a separate "regnum" (kingdom) within the empire and as a separate people, just as the Saxons and Gascons might be. Frisian "identity" aided in the control of trade routes, as small Frisian communities settled throughout the empire (and in Scandinavia and England as well).

5. I am not quite sure what you mean here, but I think this may just be a confusion in terms. The Viking Age is a distinct chronological period, (as noted above). In terms of its end, this is largely due to major political changes across Europe, especially in Scandinavia, but certainly in Frisia as well. And by the 11th century the term "Frisia" had largely fallen out of use anyhow as the regnum "devolved" into powerful counties.

6. The Frisians were a Germanic people so there were certainly some similarities, but they were also quite different. For one thing they were a part of the most powerful political entity of the period, were far richer and more political unified and stable. That being said, a sword is a sword, they both used them. Scandinavian warfare wasn't actually as "distinct" as is often thought, they used swords, armor, etc. The advantage they had was typically surprise. Archaeologically, they are fairly distinct in style and material, however. We have no difficulty telling whether a sword found in a Frisian river is Frankish/Frisian or Scandinavian.

7. I think I've answered this before but yes, Frisian and Old Norse (and Old Saxon and frankly Old Franconian as well) were probably mutually intelligible. Viking chieftains actually settled in Frisia as rulers for periods of time throughout the 9th and 10th centuries, and as stated above Frisian traders were quite active in Scandinavia. We even have references to traders being used as diplomatic go-betweens for Danish and Frankish kings.

8. He was Danish, or at least Scandinavian. The confusion arises from the fact that by the time of the Great Army Vikings had been quite active in Frisia and had even (as I noted above) settled in certain areas and at times been granted land by Frankish kings in an attempt to control their predations. The Great Army thus probably had groups of Scandinavians who had previously been active in Frisia, but it was not a "Frisian" force.

9. Yes, and yes. But in the period in question they were trade ships not "viking ships" They were not clinker built (i.e. they were not long ships) but more often resemble barges. But again, Frisians were masters of the river ways and seas.

10. We have no way of knowing numbers, but its hard to believe that some Saxons didn't flee west. That being said, Saxony remained a distinct regnum and the Saxons remained a distinct people with their own laws and leaders. The Frisians and Saxons were neighbors and in many ways very similar (especially those Saxons along the coasts) but they didn't "merge." Although following the 804 deportation of the Nordliudi Saxons from beyond the Elbe it could be that Charlemagne settled some of these peoples in Frisia.

So there we go! I hope these answers are helpful. Again just to re-iterate. Frisians began as a germanic, piratical people settled along the coasts of the modern Netherlands, slowly formed into a kingdom (or perhaps even kingdoms) which was then absorbed (forcefully) into the Frankish Empire. They were widely known for teir maritime activities, first as pirates but by the end of the 8th century primarily as traders. They had frequent contact with Scandinavia and Frisia was subsequently frequently attacked by and even settled by Scandinavian pirates and chieftains.

Sources:

• The most important work on the Frisians is Stéphane Lebecq's Marchands et navigateurs frisons du haut moyen âge though you'd have to know French to read it.

• Ian Wood's The Merovingian North Sea and The Merovingian Kingdoms both have info on early Frisia, as do many of his articles.

• H.A. Heidinga's Frisia in the First Mellennium is a nice quick intro.

• In terms of primary sources, check out the Royal Frankish Annals, the Life of St. Willibrord, the Life of St Boniface, The Life of St Willifrid, the Annals of St Bertin. All of these are in translation.

Happy Frisianing!