some time ago I blogged on literacy as the child of accountancy, the argument being that if you start to need to count things, be it how much grain and oil you have stored, or how many men you can reasonably call on in case of conflict, you need a means of recording this, and that means literacy, as seen in the Minoan greek stock taking lists from Knossos, or indeed the 'Catalogue of Ships' from the Iliad.
The Senchus Fer nAlban is such a text - as well as listing the genealogies of the Kings of Dal Riata it lists the territorial divisions, of Dal Riata and how many boats (seven benchers - even gives us an estimate of the size of early Gaelic galleys) and men can be raised in case of raiding or conflict, and indirectly an estimate of population.
We of course see a similar sort of thing with the Mercian Tribal Hidage, which again could be used as a basis for tax assessment or an army levy, and interesting for what they tell us about the organisation of a society, not just in terms of individual units, but in general organisation.
We lack substantial records from the early medieval period in the British Isles - no charters to speak of, and a few battle poems, giving a view of society being ridden by conflict and disorder.
The times may have been insecure but the existence of these documents suggest that there was more organisation, planning and structure than previously thought ...