Welsh lands, Welsh law; in the Marches, Marcher law. 12T These engagements 
had no permanently stabilizing effect on political relations, which 
reached another crisis early in the reign of Edward I. A brief period of war 
was terminated by the Treaty of Aberconway (1277). This instrument contained 
the general stipulation that controversies between the Prince of Wales 
and anyone whatsoever were to be decided by the regional law of the place 
where they arose, but provided in another clause that if the Welsh prince 
wished to claim right in lands which others besides the King had acquired 
(excepting only the four cantreds ceded by the treaty) the King would show 
him full justice according to the laws and custom of those parts in which the 
lands were. 
In January, 1278, the King appointed commissioners of oyer and terminer 
to settle the claims contemplated by the treaty, and it immediately became 
apparent that this document was inadequate, chiefly because it failed to settle 
precisely the regional ambit of Welsh and Marchen law and took no account 
of the personal principle. The various conflicts problems which beset the commission 
have been well discussed by other writers. 128 We are concerned here 
only with the suit between Llewellyn, Prince of Wales, and his enemy 
Gruffydd ap Gwenwynwyn over Arwystli, because it was here that the fundamental 
question of judicial competence was raised. 
Llewellyn, appearing by attorney in July, 1278, made his claim to the lands 
before the commissioners, and after preliminary sparring over the propriety 
of such appearance, the case was continued to the Michaelmas sitting. But 
before this event the cause was adjourned before the King himself at Rhuddlan. 
Here, according to Llewellyn, 129 the King conceded that Welsh law should 
govern, and Welsh judges actually were brought in to act, when inexplicably 
the case was remitted to the commissioners. It should be noticed that at this 
session the opportunity existed of following the Gascon precedent of associating 
the expert in an alien law. Why this course was not followed we do not know. 
When the case was resumed before the commissioners, the claimant de- 
manded that the defendant be attached according to Welsh law, on the 
grounds of the Welsh condition of both parties, because the lands were pure 
Welsh (mere est Walensica) and because of the clause in the treaty. Gruffydd 
in replication asserted that he was a Marcher baron holding the disputed land 
in barony of the King and so ready to proceed by the common law. He further 
127 The engagements listed are in Davies, The 
Welsh Assize Roll 1277-84, 3. 
123 In particular by Davies, op. cit. An earlier 
account is in Lloyd, Edward the First's Commission 
of Enquiry of 1280-81, 1 Cymmrodor, 
257. The latest discussion (2 Powicke, 
King Henry 111 and the Lord Edward, c. xv 
et seq.) is strongly biased in favor of Edward's 
power politics. 
129 This stage of the proceedings was not recorded 
and comes from allegations of Llewellyn, 
Davies, op. cit., 135.