This paper examines the issues involved in establishing the chronology of elements referring to landscape features. Much work has been done on the Irish topographical lexicon in recent decades, notably by Prof. Liam Mac Mathúna, whose approach is rooted in word-field studies. His research has focussed on common nouns occurring in Old Irish and Middle Irish texts. This paper takes a complementary approach by asking what further light the evidence of place names can shed on the topographical lexicon. It also attempts to establish the outlines of a (largely relative) chronology with a view to gaining insights into the origins and primary meanings of these elements. Some elements which are known chiefly through place names, and have therefore tended to be neglected in etymological and semantic studies, are examined (e.g., mionnán, ‘cliff, pinnacle’, málainn, meaning uncertain). Tautological names are discussed as a resource which can help to construct a relative chronology. Some difficulties concerning the date of the first appearance of certain elements in Irish (e.g., cnoc, ‘hill’, sceir, ‘rock, reef’) or regarding their origin (e.g., gaoth, ‘inlet’ and poll, ‘hole, pool, bay, stream’) are also examined.