Nepos (Latin for ‘nephew’) of Montauban was a thirteenth-century scholar and practitioner of law from southern France. Until recently just two things were known about him. One was that at the end of the 1260s he wrote a major work of jurisprudence, a treatise on defences in law. Its stated aim was ‘to teach defendants how to flee’, hence its colourful title, Liber (or Libellus ) fugitivus , ‘The Fleeing Book’ or more loosely ‘The Escape Book’. The other is that he officiated at the same time, in the second half of the 1260s, as a judge in the lands of Alphonse of Poitiers, the Capetian count of Toulouse. But our knowledge is changing. First, in 2005 Giovanna Murano demonstrated that Nepos was not the primary author but only the redactor of the Liber fugitivus . Secondly, though hardly anything has been known about Nepos's life, this chapter will show that the archives of his hometown and inquisition records can be used to establish a surprising number of facts about him. The most important new biographical information is that our judge, scholar and ‘teacher of legal defence’ played a very active role in the inquisition of heresy. As a young man he was a leading collaborator of the Dominican Friars Bernard of Caux and John of St Pierre in their mass trials in the mid-1240s. The two inquisitors directed their ecclesiastical court procedures against the inhabitants of the Lauragais, a fertile and densely populated rural region to the east of Toulouse. Although their inquisition activities count among the earliest in the middle ages, they are also the largest in scope, as they involved several thousand men and women. And for over a year Nepos was one of the most important assistants in this huge endeavour.

It may strike us as odd that a man who had given his assistance to such a large-scale prosecution of people for heresy went on to redact, roughly two decades later, a juridical treatise that was openly intended to ‘help defendants to flee’. Is the contradiction real or only apparent? Whatever the answer, the case of Nepos appears interesting enough in the context of a discussion of ‘inquisition and knowledge’ to justify systematically establishing what we know of his life.

In the following, we shall first give a summary of recent research on the Liber fugitivus (section 1).