You have to go back seven and a half centuries - to some years before 1283 - to find Welsh patrols on their borders ready to stop English "intruders".
But now police in north Wales have said they will "advise and explain" to English holidaymakers, heading for the delights of Snowdonia or the Welsh coast, that they are breaching the "essential journeys only" rule. Fines will ensue if those English visitors do not take the Welsh constabulary's advice.
This is surely the most standout development in a parting of the ways between London and its home rule governments in Cardiff, Edinburgh and Belfast, in the fight against coronavirus. The devolved administrations have all found Prime Minister Boris Johnson's key-note messages on phasing out of the lockdown too confusing, too vague, and too risky.
First it was Brexit, now it is coronavirus. The four parts of the United Kingdom - England, Scotland, Wales and Northern Ireland - are increasingly differentiated. It again raises questions about prospects for Irish unity in the medium to longer term.
The 'Welsh story' has long been neglected on this side of the Irish Sea. Their relationship with London is even older than ours and the history books date the Welsh conquest by the English King Edward I at 1283.
The formal legal amalgamation of both entities dates from 1542. But across the centuries the Welsh found many different ways of maintaining their identity and pride not least by domination from within. Randomly we can pick the Tudors, Lloyd George, and Aneurin Bevan, father of the UK's national health service, as just a few standout examples.
Granted when the UK as a whole voted to 'Leave' the EU on June 23, 2016, the voters in Wales went with the majority English vote. In fact, Wales exactly mirrored the overall UK verdict of 52pc Leave and 48pc Remain, leaving many Europhobes in England glorying that this was despite the Welsh receiving the highest per capita level of EU grant aid.
It has often been pointed out since that, in sharp contrast, the two other legal components of the UK voted in the majority to Remain. Political leaders in Scotland (62pc) and Northern Ireland (56pc) have repeatedly raised the issue, and warned of the perils of being lugged out of the EU, and losing single market and customs union benefits, against the people's will.
In Cardiff, there have been many post-mortems on a mismanaged Brexit campaign. But there has also been a new-found determination to project Wales as an autonomous entity. Indeed just before the coronavirus erupted in earnest, the Cardiff minister for international relations Eluned Morgan was in Dublin on a mission to raise the profile of her country here. She pointed out that Irish-Welsh links, dating back to that Welshman, St Patrick, are set to be strengthened.
Management of the coronavirus crisis fell to the devolved parliament and administrations in Belfast, Cardiff and Edinburgh under the home rule arrangements fixed in 1998, and variously expanded since then, which gave each area powers over areas like health, transport and policing.
Welsh First Minister Mark Drakeford and his Scottish counterpart, Nicola Sturgeon, accused Mr Johnson of stoking up confusion by not making it clear enough that his changes applied to England only.
It made the job all the more difficult for Welsh police stopping regular English visitors and trying to make them realise Wales was operating much tighter rules.
Northern Ireland First Minister Arlene Foster announced a conservative five-step plan for easing its lockdown which did not give specific dates. Her colleague, Michelle O'Neill, stressed that the North would try to co-ordinate as closely as possible with Dublin.
It is a complex business in itself - but with potential for many permanent changes in the medium to longer term.