Through outlaws, robbers, thieves and malefactors, mounted and on foot [...] wandering by day and night, so many and great homicides and robberies were done that no one with a small company could pass through those parts without being taken and killed or spoiled of his goods [...] and no religious or other person could pass without being taken or spoiled of his goods.

So proclaimed Edward I of England at the end of the 13th century, a fairly typical medieval presentation of the threats to the traveller. The question of just how typical this was has perplexed historians, if for no other reason than the basis of evidence for most of the medieval period is not statistical court records but literary writings, and,

it is precisely the literary nature of the sources that makes it so easy to exaggerate in our minds the number of medieval psychopaths. ^1

There are occasional glimpses through laws and edicts, for example Anglo-Saxon laws like Laws of Wihtræd of Kent which required particular stretches of forest roads to have trees cleared to a certain depth or which required travellers to stay within the road and not at the edges and not to stop, for such travellers were then no longer protected by law.

But, the principle sources through to the 15th century are literary: ecclesiastical chronicles. For this reason, the victims in our sources are dominated not by the day to day lives of peasantry, but by the following groups:

1. religious travellers, ie pilgrims, increasingly through the high middle ages with the growing industry of pilgrimage tied to the growth of apostolic forms of observance and the increase of penitential activity

2. merchants, increasing in traffic through the high middle ages as a product of the commercial revolution

3. trains of nobility and bishops

The challenge is who in these literary sources can we identify as the latrones (robbers) and praedones (predators) who prey on the travellers?

Popes and monarchs complained about attacks on pilgrims, and the Papacy for its part ordered certain measures to make safe places on long lonely stretches of popular pilgrimage routes - safe houses at certain distances along the way, funded by local churches and monasteries. Here these attacks seem to be not so much organized crime as opportunistic theft. ^2

However, organized crime was an issue for travellers. There are great numbers of complaints about 'illegal tolls' being charged to pilgrims, and in fact the first 'guide book' for pilgrims warns to avoid certain bridges on the Via Compostela, the most popular route in the high middle ages.

Chronicles are filled with stories like this one from always very entertaining abbot Guibert of Nogent writing in Normandy at the end of the 11th century. Here we writes about Theudegaud,

a pestilent fellow, a bondman of the church of the Blessed Vincent, but for a long time a provost of Enguerrand of Coucy, who being set over the collection of tolls paid for crossing the bridge called Soord, sometimes watched until there were only a few travellers passing, and having robbed them of all their property, in order that they might make no complaint against him, threw them into the river with a weight round their necks. How often he had done this, God only knows. The number of the thefts and robberies being more than any one could count, the unchecked wickedness of his heart, and one as might say, was displayed also in the truculence of his looks.

Here we see the reality of organized banditry in the high middle ages: nobility and their quasi-legal hangers-on. These organized bandits set up tolls on bridges, assaulted trains of other nobles and ecclesiastics with whom they had feuds, and helped to create the image of the lawless middle ages. The same nobles were the target when King Rudolf I of Germany tried and failed to 'smoke out' the robber knights [Raubritter] from their robber castles in Thuringia in 1289.

Some jurisdictions had legal methods of resolving theft of moveable property. Although trial by ordeal was generally fading (or even outlawed) for many crimes by the 13th century, English law provided for trial by battle for resolving cases of theft. In the middle of the 13th century the Hampshires saw trial by battle between 'highway men' and certain nobility who had been assaulted and robbed. ^3

^1 Timothy Reuter, "The insecurity of travel" in Medieval Polities and Modern Mentalities (Cambridge University Press, 2006)

^2 For details of dangers to pilgrims and papal edicts in response see: Diana Webb, Pilgrims and Pilgrimage in the Medieval West (I.B.Tauris, 2001)

^3 See Michael Clancy, ‘Highway robbery and trial by battle in the Hampshire eyre of 1249’, in R. F. Hunnisett and J. B. Post eds., Medieval Legal Records Edited in Memory of C. A. F. Meetings, 2nd ed. (London, 1980)

In Iceland, it was actually a bit of an issue! I'll direct you to this answer I gave in the a similar thread about outlawry, banditry, and how Icelanders dealt with it. If you have any other questions, or want elaboration, please ask!

hi! there's more on medieval banditry in these posts

• Medieval and "Fantasy" stories often use the trope of a bandit attack on a village. Was this a common thing anywhere in the world?

• How big of a problem were bandits in the middle ages and early modern period?

• How safe was medieval Europe?

• Were there "gangs" in the ancient era and medieval era of history?

Does anyone know anything about the raider stronghold of Fraixnet in 10th century Occitania that OP mentioned?

Google gave me no search results.