The penultimate presentation at last term's IHR Earlier Middle Ages seminars was given by Morn Capper, currently working on the Staffordshire Hoard at Birmingham Museum, although unfortunately she wasn't allowed to talk much about this at the time. Her paper was entitled "Rethinking thought and action under the Mercian hegemony: responses to Mercia c. 650-850", and was to a considerable extent (as I only realised via some reading up afterwards) a response to a view of Mercia, and Offa in particular, promulgated by Simon Keynes, especially in Changing faces: Offa, king of Mercia, History Today 14 (11) (November 1990), 14-19.
It was Simon who came up with one of the key images that Morn was, I think, trying to challenge, when he claims (p. 17):
He [Offa] might be seen as a species of Mercian octopus: his tentacles reaching out over different peoples, smothering some and poised more or less threateningly over others, but united only in the head that remained firmly in the West Midlands.
There were several other points Simon made in this article that Morn was implicitly replying to. Simon pointed out that charters that refer to Offa as rex Anglorum are C10 forgeries, but Morn mentioned the Ismere charter of 736 which calls Athelbald of Mercia rex Britanniae and was arguing that there are other contemporary hints of the power of the Mercian king, such as Felix's Life of St Guthlac which sees his rule as providential.
Morn was also trying to look at the possibility of agency by regional rulers, arguing that they can be seen as negotiating their submission to Mercia, instead of simply being "smothered" by it. She cited the example of Sebbi of Essex, abdicating to become a monk in 694 and using grants of lands to monasteries to secure his children's prospects. Choosing Mercian lordship allowed East Saxon kingship to survive.
It's also possible to see differing choices by regional nobility in their response to Mercian kings. The Hwiccans engaged with Mercian rule and their royal line benefited from this. In contrast, there's very little evidence of East Anglian secular leaders engaging with the Mercians. Some royal lines may also have effectively gone "underground" for generations, e.g. the East Anglian royal line re-emerges after the death of Offa.
Finally, Morn was arguing that Mercian kings weren't as autocratic as has sometimes been made out. We can see the importance of church councils from 781 onwards, and the Mercian army should also be seen as a political institution. Indeed she thought that it was the army that raised Coenwulf to kingship, but also added that military defeat could lead to a spiral downwards of loss of power, e.g. as happened in the 820s.
Simon's image of the Mercian octopus implies top-down, oppressive control. If I understand Morn correctly, she's arguing for more negotiation between the centre and regions/localities, a model that's now very familiar in Carolingian historiography.
However, there were a couple of points Morn mentioned in passing that do challenge some of our understanding of early medieval polities more generally. One is that you have some moneyers minting across rulers and during rebellions: even though Offa is one of the first kings to have portrait coins (before the Carolingians did), there were limits to kings' powers. Secondly, there is almost no pottery evidence in western Mercia till around 1000 AD. More generally, there seems to be a contrast between a monetized periphery of Mercia towards the east and south coasts and a heartland, where, for example, the archbishop of Lichfield was not minting coins.
These facts call into question two of the main types of evidence that have been used for measuring the power and complexity of a state: ceramics and coin evidence. We know about the wealth and power of Mercia from other textual and archaeological evidence: if we didn't have that, would we conclude that the Mercians must still have been largely at a stage of small-scale kingship and what Chris Wickham calls the "peasant mode of production"? Are our more general measures of economic and political development as robust as we would like to hope? It's one of the many interesting questions that Morn's paper raised.