Ffeil NLW MS 21290E. - Llawysgrif Llewelyn Sion,

Another of the 'long books' of Glamorganshire copyist, Llywelyn Siôn (cf. Llanstephan MS 134, 'Llyfr Hir Amwythig'; NLW MS 970, known as the Merthyr Tydfil MS or 'Llyfr Hir Llywarch Reynolds'; and 'Llyfr Hir Llanharan', in the Cardiff Central Library). The first poems in this collection are wanting and those we have are numbered from 48-[528], but there are several gaps and the text is often imperfect or incomplete owing to the very fragile and decayed state of the manuscript. Many of the poems are also to be found in the manuscripts referred to above, although not always in the same sequence.
The poets whose work is represented include the following: Bedo Aeddren, Bedo Brwynllys, Bedo Phylip Bach, Dafydd ab Edmwnd, Dafydd ap Gwilym, Syr Dafydd ap Phylip Rhys, Dafydd ap Rhys, Dafydd Benwyn, Dafydd Epynt, Dafydd Goch Brydydd, Dafydd Gorlech, Dafydd Llwyd ap Llywelyn ap Gruffudd, Dafydd Llwyd Mathau, Dafydd Nanmor, Deio ab Ieuan Du, Deio Lliwiel, Edwart ap Rhys, Gronw William, Gruffudd ab Ieuan Hen, Gruffudd ab Ieuan ap Llywelyn Fychan, Gruffudd ap Dafydd Fychan, Syr Gruffudd Fychan, Gruffudd Gryg, Gruffudd Hiraethog, Guto'r Glyn, Gwerful ferch Hywel Fychan, Gwilym ab Ieuan Hen, Gwilym Tew, 'Hopgin thom phylip', Huw Cae Llwyd, Mastr Huw Pennant, Huw Robert(s) Lên, Hywel ap Dafydd ap Ieuan ap Rhys, Hywel ap Rheinallt, Hywel Swrdwal, Ieuan ap Huw [Cae Llwyd], Ieuan ap Hywel Swrdal, Ieuan ap Rhydderch ab Ieuan Llwyd, Ieuan Deulwyn, Ieuan Du'r Bilwg, Ieuan Dyfi, Ieuan Ddu ap Dafydd ab Owain, Ieuan Gethin ab Ieuan ap Lleision, Ieuan Leiaf, Ieuan Llawdden, Ieuan Rudd, Ieuan Rhaeadr, Ieuan Tew Brydydd, Ieuan Tew Brydydd Ieuanc, Iolo Goch, Iorwerth Fynglwyd, Iorwerth Hen, Lang Lewis, Lewis y Glyn, Syr Lewis Meudwy, Lewis Môn, Lewis Morgannwg, Llywelyn ab Ednyfed, Llywelyn ap Hywel ab Ieuan ap Gronw, Llywelyn fab Moel y Pantri, Llywelyn Goch ap Meurig Hen, Llywelyn Siôn, Maredudd ap Rhoser, Mastr Harri, Mathau ap Llywelyn Goch, Meurig Dafydd, Morgan Elfel, Morgan Powel, Morys ap Hywel, Morys ap Rhys, Owain ap Llywelyn ap [y] Moel, Syr Phylip Emlyn, Robert Leiaf, Robin Ddu, Rhisiart ap Rhys, Rhisiart Fynglwyd, Rhisiart Iorwerth, Syr Rhisiart Lewis, Rhys ap Harri, Rhys Brychan, Rhys Brydydd, Rhys Goch o Eryri, Rhys Goch o Fochgarn, Rhys Nanmor, Syr Rhys o Garno, Rhys Pennarth [sic], Rhys Trenn, Sils ap Siôn ap Hywel Gwyn, Siôn Cent, Siôn Ceri, Siôn Mowddwy, Siôn Phylip, Siôn Tudur, 'Thomas ap sion kati', Thomas Brwynllys, Thomas Celli, Thomas Derllysg, Thomas Gruffydd, Thomas Llywelyn, Tudur Aled, Tudur Penllyn, Wiliam Cynfal, Wiliam Egwad, Wiliam Llyn.