Fosterage, the practice of a family bringing up a child not their own, differs from adoption in that the child's parents, not the foster-parents, remain the acknowledged parents. In many modern western societies foster care can be organised by the state to care for children with troubled family backgrounds, usually on a temporary basis. In many pre-modern societies fosterage was a form of patronage, whereby influential families cemented political relationships by bringing up each other's children, similar to arranged marriages, also based on dynastic or alliance calculations.Children continue with the fosterer perhaps six years, and cannot, where this is the practice, be considered as burdensome. The fosterer, if he gives four cows, receives likewise four, and has, while the child continues with him, grass for eight without rent, with half the calves, and all the milk, for which he pays only four cows when he dismisses his Dalt, for that is the name for a foster child. Fosterage, the practice of a family bringing up a child not their own, differs from adoption in that the child's parents, not the foster-parents, remain the acknowledged parents. In many modern western societies foster care can be organised by the state to care for children with troubled family backgrounds, usually on a temporary basis. In many pre-modern societies fosterage was a form of patronage, whereby influential families cemented political relationships by bringing up each other's children, similar to arranged marriages, also based on dynastic or alliance calculations. This practice was once common in Ireland, Wales, and Scotland. In medieval Highland society there was a system of fosterage among clan leaders, where boys and girls would leave their parent's house to be brought up in that of other chiefs, creating a fictive bond of kinship that helped cement alliances and mutual bonds of obligation. In his A Journey to the Western Isles of Scotland (1775), writer Samuel Johnson described the fosterage custom as he saw it practised. Fosterage or 'fostering' is frequently referred to in the medieval Sagas of Icelanders. Original family ties and rights of inheritance were not affected, nor was it required for the fostered child to be an orphan or for the biological father to be deceased. Moreover, the fostering of another man's child was regarded as a source of honor to the birth father; and conventionally the fostering party was of inferior social status to the biological father. An exception to this convention is found in Njáls saga, where Njál Thorgeirsson, a very prominent man, fosters Hoskuld, the son of Thrain Sigfusson, after the death of Thrain in battle. Portions of Ireland, Scotland and the Hebrides were ruled for long periods of time by Norse invaders during the Middle Ages; but it is unknown which culture was the original source of the custom of fosterage. In Ancient Ireland, ollams taught children either for payment or for no compensation. Children were taught a particular trade and treated like family; their original family ties were often severed. There was similar custom in the Caucasus, called Atalik - ru:Аталычество.