The later codes show his concern with threats to social order, especially robbery, which he regarded as the most important manifestation of social breakdown. The first of these later codes, issued at Grately, prescribed harsh penalties, including the death penalty for anyone over twelve years old caught in the act of stealing goods worth more than eight pence. This apparently had little effect, as Æthelstan admitted in the Exeter code: "I King Æthelstan, declare that I have learned that the public peace has not been kept to the extent, either of my wishes, or of the provisions laid down at Grately, and my councillors say that I have suffered this too long." In desperation the Council tried a different strategy, offering an amnesty to thieves if they paid compensation to their victims. The problem of powerful families protecting criminal relatives was to be solved by expelling them to other parts of the realm. This strategy did not last long, and at Thunderfield Æthelstan returned to the hard line, softened by raising the minimum age for the death penalty to fifteen "because he thought it too cruel to kill so many young people and for such small crimes as he understood to be the case everywhere". His reign saw the first introduction of the system of tithing, sworn groups of ten or more men who were jointly responsible for peacekeeping (later known as frankpledge). Sarah Foot commented that tithing and oath-taking to deal with the problem of theft had its origin in Frankia: "But the equation of theft with disloyalty to Æthelstan's person appears peculiar to him. His preoccupation with theft—tough on theft, tough on the causes of theft—finds no direct parallel in other kings' codes."