To inform the consideration of The Inventory of Historic Battlefields in Wales , documentary and historical research was commissioned on the 1461 battle of Twthill and the resulting research report provides a detailed overview (Border Archaeology).

The battle of Twthill fits into one of the periods of extreme political instability, the `War of the Roses? which accompanied the political fluctuations of the mid-fifteenth century. Although the battle was little more than a skirmish, the result was significant, the Yorkists had succeeded in destroying the last major Lancastrian field force in Wales and had forced their principal leaders, Henry Holland the Duke of Exeter and Jasper Tudor, Earl of Pembroke, to flee the country.

The battle itself is very poorly documented; no reference to it has been found in contemporary or near-contemporary chronicles of the period and consequently very little appears to be known concerning the course of the battle, the events immediately preceding it and its aftermath. The only specific reference to the battle and its location occurs in a list of persons attainted for treason at the Parliament held on 4th November 1461, which notes:

Translation: 'Henry duke of Exeter, Jasper Earl of Pembroke and Thomas Fitzhenry late of Hereford, esquire, at a place called Twthill (Tutehill) beside the town of Caernarfon in Wales, on the Friday after the feast of the translation of St Edward last (16 October 1461) raised war against our same sovereign, intending then and there to proceed to his destruction by treacherous and cruel violence, against their faith and allegiance' (Horrax).

It is possible that the Lancastrians were encamped at Twthill before proceeding to attack the town of Caernarfon, although this cannot be verified from the available evidence. Twthill is identifiable with the steep, partially wooded outcrop within the modern town of Caernarfon (SH 4822 6303), 400m to the north-east of the medieval walled borough. On the summit of the hill are traces of a rock-cut ditch, described by the RCAHMW Inventory (1960) as probably being pre-Roman in date, although the possibility that it could represent a medieval motte and bailey earthwork cannot be discounted (RCAHMW, 158b).

RCAHMW (Battlefields Inventory), Jan 2017

Bibliography
Border Archaeology, Twthill (October 16th 1461): Documentary and Historical Research Report (2009).
Horrox R. (ed.), `Edward IV, Parliament of 1461, Text and Translation?, The Parliament Rolls of Medieval England, Given Wilson et al (ed). (CD Rom Scholarly Digital Editions, Leicester, 2005), vol. 478a.
RCAHMW, An Inventory of the Ancient Monuments in Wales and Monmouthshire: V County of Carmarthen (HMSO, London, 1960).