With kinship being an essential element in early Celtic legal systems, it seems likely that artificial kinship, in the form of fosterage, was also an important element of these early customary laws. Evidence for the exchange of children as hostages can frequently be found in historical sources, which, as most of them were the children of important nobles, must have been educated during this time, as they would have been expected to become important nobles themselves in the future. Similarly, the reference in Caesar that many Gauls send their children to study druidry, which is best to be studied in Britain at its alleged point of origin, together with his remark that the Gauls do not suffer to be seen with their children in public, might indicate that fosterage practices were widespread. This would seem to be supported by the fact that fosterage was important in both early medieval Irish and Welsh societies, and that there is a cognate terminology in Irish and Welsh for the foster-father/teacher, allowing to reconstruct a Celt. *"altros", 'nourisher, foster-father, teacher', as well as close friend/foster sibling, from Celt. *"komaltros", 'jointly nourished, co-fostered, alumni'. Fosterage networks, establishing artificial kinship and thus political and information exchange networks also are a good explanation for the spread of some aspects of 'Celtic' material culture, like e.g. La Tène art.