I think that it is very difficult to understand the differences between Roman and Celtic culture in Britain after the withdrawal of direct Roman influence. Indeed, even in Wales which is seen as a predominantly Celtic region, the importance of not only Roman rule but iconography and symbols can be seen with the building of Caernarfon Castle in 1238, in which Edward I chose Eagles to top his towers and incorporated features of Roman or Byzantine architecture in order to establish legitimacy. I have also heard that around the coast of the South West, many people continued to associate themselves with the Roman heritage, utilising symbols such as dragons which had been familiar to them from the Roman period, although I cannot remember where this thought springs from. Furthermore, towns continued to be known by their Roman names such as Eboracum (York).

The legend of King Arthur is also integral to the Brythonic story, and yet draws a great deal from Roman culture. His name may well have originated from the Etruscans, whose own culture was adapted by the Romans, and then further modified by the Britons. This can also be seen in the history of St Patrick, whose existence is evidence of the Church in Britain, which was established by the Romans. In his 'Letters to Coroticus' Coroticus is a British Tyrant who is decidedly Roman, at least in terms of his name and use of Latin.

I personally subscribe to the school of thought that no dry cut change occurred to culture when the Romans first arrived or eventually left, and that the culture became Romano-British. This is compounded by evidence from Gildas, an Early British writer, who used Latin. It is true that there was a rejection at least in part of the Roman ways, indeed by this time across the Empire the distance between early and contemporary Roman culture can hardly be underestimated.

I would recommend researching Romano-British culture and Sub-Roman Britain. Here is a pretty good essay discussing some issues you might be interested in citing Gildas and St Patrick, as I have: http://www.the-orb.net/encyclop/early/origins/rom_celt/romessay.html

The two recent studies you should see for late roman Britain are Robin Fleming, *Britain after Rome *(2011), and James Gerrard, *The ruin of Roman Britain *(2013). Both authors discuss fifth-century Britain in economic and military terms, and both are concerned with the kinds of social transformations that follow the breakdown of Roman government. Fleming argues that Britain's economy collapses, leaving nothing but peasant farmers who wouldn't have ever been participants in Roman high society. Gerrard has a more positive view of the economic situation, but also focuses on the role of local agrarian communities in driving social transformation.

You might also benefit from Alex Wolf's discussion of the textual evidence for social change in late Roman Brtiain.

In all these cases, the situation is more complex than simple reversion to pre-Roman social structure. It would be more accurate to say that elite Roman culture was radically transformed or abandoned, to be replaced in some regions by the military Roman identity of mercenary groups like the Saxons, or a new kind of semi-Roman elite in Wales, and - in general - a devolution to the hybrid Roman-British culture that had developed among farmers and peasants during 400 years of occupation.

You see lots of different responses and social changes, depending on what region you examine. The archaeological excavations at Wasperton (near the border between Wales and what would become England) revealed a community that continued for centuries after Rome with a fair measure of continuity (Carver et al 2009, Wasperton). The community didn't immediately revert to a Celtic identity after it stopped being Roman, but slowly blended changing burial practices and cultures as Britain became less Roman.

Similarly, rural communities in Northern England seem to have preserved their place in a landscape that had a lot of continuity with both Roman and pre-Roman settlement patterns - it seems the Romans had blended in with older systems rather than flat-out replacing them, and those systems continued to structure settlement patterns after the Romans left (see chapter 3 in this volume), and the ongoing research of the Landscape Research Centre.

In other parts of England, settlement patterns did shift rapidly, Roman estates were broken up, and new field divisions appeared. Simon Draper discusses this for Wiltshire.

Adam Rogers discusses the changing landscapes of cities, which were recycled for use as new kinds of elite power centers as Roman authority started to wane.

So you're really looking at a variety of responses to a breakdown of central power, not a simple reversion to pre-Roman identities. Different parts of Britain go different directions, one of which is the shift toward German North-Sea identities in south-eastern Britian, possibly as a rejection of any connection to Roman politics (Guy Halsall recently coined the phrase, 'undead Roman Empire' to describe the lingering Romanness in parts of Britain, arguing that south eastern Britain remained culturally Roman until the late fifth century, at which point it rejected that identity; see this blog post and his interesting and useful book, Worlds of Arthur). On the whole, however, the research points toward post-Roman Britain as a period of invention of new identities (some of which were re-imagined from pre-Roman culture, but most of which used Roman culture as a starting point for the creation of something new), and not simply a reassertion of pre-Roman social structures.

So, we're not here to do your homework for you, but pointing you toward sources is a fine use of the sub. Can you tell us what sources you've been using to construct your argument, the scope of it, and what part(s) of Britain you're looking at? The Ordovices were only one tribe, in modern-day Wales if I remember correctly, so their experience may not be modal or indicative of the wider Celtic experience.

You may want to look at Martin Millet's Romanization of Britain, if you can. There is quite a large bibliography on this topic but that is a good start.

On a broader level, I think you will have something of an uphill battle describing the Roman invasion as genocidal. Even if you wanted to take Tacitus entirely at his word, the Ordovices are only one nation. The experience of invasion varied a great deal among the various kingdoms and peoples of Britain.