What is truly timeless? This book explores the language of eternity, and in particular two ancient Greek terms that may bear the sense of eternal : aiônios and aïdios. This fascinating linguistic chronicle is marked by several milestones that correspond to the emergence of new perspectives on the nature of eternity. These milestones include the advent of Pre-Socratic physical speculation and the notion of limitless time in ancient philosophy, the major shift in orientation marked by Plato s idea of a timeless eternity, and the further development of Pre-Socratic insights by Epicurean and Stoic thinkers. From the biblical perspective, the intersection of Greek and Hebrew conceptions is reflected in Septuagint, as well as new inflections in popular terminology in the Hellenistic and Roman periods, and in the role of eternity in the theology of the New Testament. The profound cross-fertilization of Christian and classical philosophical conceptions in the works of the Church fathers and their contemporaries is explored, bringing the topic into the Patristic period. Christian theology in the first five centuries of the Common Era and its choice of vocabulary prove to be most revealing of larger doctrinal commitments. Above all debate raged on the question of eternal damnation versus the idea (deemed heretical in the Christian church after the formal condemnation of Origenism) of apocastastis or universal salvation - that is, the belief that the wicked are not condemned to eternal punishment but will eventually be included among the saved. Terminology for eternity is often at the core of how these issues were debated, and helps to identify which writers inclined to one or the other view of the matter.