Before R.A. Markus became a historian, he was preparing to become a Dominican friar, and he might never have become a historian if it wasn’t for his novice-master. When he arrived at Blackfriars, Oxford, in 1950, it was decreed that he ‘was not to read any philosophy, just to bring home that [he] was no longer a doctoral student’. The writings of St Augustine of Hippo were, however, deemed to be acceptable reading for the young novice. Thus began a consequential intellectual encounter.

Robert Austin Markus was born Róbert Imre Márkus 100 years ago in Budapest. Both his parents were Jews, his father an engineer and his mother a ceramicist. His father had converted to Lutheranism but then reverted: he did not think it right to abandon his co-religionists at a moment of intensifying antisemitism. In 1939, seeing what was to come, the family left for England. Markus’ ‘main aim’, he later recalled, ‘was to become thoroughly English’: Róbert Imre was eventually to become Robert Austin. He went to study chemistry at Manchester at the behest of his more practically-minded father. But his heart was in philosophy, and he was able to jump ship for his MA, which he completed under the supervision of Dorothy Emmet (who supervised another of the great Catholic-convert intellectuals of Markus’s generation, Alasdair MacIntyre). The subject of Markus’ dissertation was the philosopher Samuel Alexander, the first Jewish fellow of an Oxbridge college, and he moved further back in time, to the Renaissance, for his PhD. In 1946 he became a Catholic, and the rest of his family swam the Tiber with him.

It was not (one assumes) the novice-master’s injunction on his reading philosophy that eventually dissuaded him from taking final vows as a Dominican friar, but rather his reacquaintance with an old friend, Margaret Bullen, whom he desired to marry. His politics were left-wing – he was a supporter of the Campaign for Nuclear Disarmament – and he was also firmly on the liberal end of the Catholic spectrum, rejoicing at Vatican II. By that time he was in the history faculty at Liverpool, where he taught, among others, Ian Kershaw (once a social and economic historian of the late Middle Ages, now better known for his multiple-volume biography of Hitler). He held the chair of medieval history at Nottingham from 1974 until his early retirement in 1982.

Of the historians I was required to read as an undergraduate, Markus was among the most exhilarating. One of the others in that category, Peter Brown, biographer of St Augustine, holds Markus in the highest esteem: ‘he traced the subtle changes of Augustine’s mind with the precision of a master jeweller disassembling a complex watch’. In his recently-published autobiography, Brown paints Markus as a quintessential don, pipe in hand. ‘He leaned back with his head cocked to one side like an alert bird, emitting purr-like chuckles whenever he encountered a good idea.’ Brown’s admiration was reciprocated; Markus dedicated his book The End of Ancient Christianity to Brown and described him, his junior by over a decade, as ‘my teacher’.

It is not surprising that Markus, a Catholic convert, was drawn to conversion as a historical theme. Augustine is the Christian convert par excellence, whom practically all later converts have affected to imitate; the Confessions are a candid and at times tortured exposition of the convert’s mind. In The End of Ancient Christianity Markus reflected upon the shifting ways in which converts to Christianity were expected to treat their pre-conversion beliefs, practices, and identities. He regarded this as one of the central problems inherent to Christianity as a proselytising religion: a problem that beset missionaries in the early-modern Americas, as well as relations between the church and secular life in his own day.

The concept of the ‘secular’ was the master-theme in Markus’s work. In his great 1970 exposition of St Augustine’s thought, Saeculum, Markus cast Augustine as a lone champion of intellectual humility in an age of cocksure triumphalism. Of course, Augustine ‘had no doubt that all history was in a sense God’s doing’; but, uniquely among the intellectuals of his age, Augustine was opposed to reading the divine will into the human past (except for that recorded in scripture), as other Christian historians such as Eusebius and Orosius were wont to do. Indeed, Augustine rejected attempts to predict the Last Judgement for much the same reasons. ‘Every moment’, Markus concluded, ‘may have its unique and mysterious significance in the ultimate divine tableau of men’s doings and sufferings’; but for Augustine ‘it is a significance to which God’s revelation does not supply the clues’.

Augustine’s stout refusal to play these Euesbian or Orosian games, on Markus’s narrative, had vital political implications. It was a commonplace in early Christian writing to contend that the spiritual success of the Christian faithful was somehow connected to the temporal success of the Roman Empire. Rome, they argued, was one fixture within a wider providential scene-setting: that the Incarnation was coterminous with the pax Augusta was no accident, but deliberately coordinated to the benefit of the Christian ministry. Augustine, according to Markus, wished to sever this connection. For him ‘Roman world-domination is not a preparation for the preaching of Christ’s kingdom but the achievement of “the new Babylon”’; it was, in other words, part of a secular plane of existence. In his rejection of the ‘identification of the Church’s destiny with that of the Empire’, Augustine had increased the size and scope of the ‘secular’. By then resisting the ‘divinisation of any form of social arrangement, whether existing or proposed’, Augustine’s thought was ‘of its nature politically radical’. His ‘secularisation of the realm of politics implied a pluralistic, religiously neutral civil community’; and his theology (Markus was clearly writing here against more conservative-minded Catholics) ‘should at least undermine Christian opposition to an open, pluralist, secular society’.

Markus’ history takes on a tragic tone. He obviously empathised with the Augustinian strain of thought, and despaired to find it ultimately defeated. Orosius’s perspective ‘continued to dominate the imaginations of late Roman Christians’, who insisted on viewing all events straightforwardly as an intelligible part of ‘God’s plan’. Pope Gregory the Great, who became after Augustine the principal focus of Markus’ mind, failed to learn the right lessons from Augustine, and still used the ‘language of a Christian version of a Roman imperial ideology’. In The End of Ancient Christianity Markus likewise lamented the ‘absorption of the “secular” in the “sacred”’, the ‘invasion of the City by the Desert’ as ‘ascetic norms came to penetrate far beyond the walls of the cloister’. When one reads Markus’ account of the transition from ancient to medieval Christianity, one is unquestionably reading an account of decline. The church that emerges, which leaves no room for the ‘secular’, and which, in its desperation to ‘stamp out paganisms’, did nothing but abolish customs that ‘the Roman Church had long ago come to terms with’, seems – by contrast with the church in the mind of Augustine – narrow and oppressive.

For presenting, in effect, the ‘radical’ Augustine as a forerunner to modern liberalism, Markus was heavily criticised both in his own day and ever since. And, of course he was up to something much more sophisticated than just that. Still, even in its crudest form his argument has much to recommend it, not only as it touches on history and theology but also in relation to modern political theory. If liberalism flows from an intense scepticism about the scope of human knowledge – as the writings of Hume and Smith would lead us to believe, and as Hayek most famously argued – then Augustine, or at least Markus’ Augustine, can be counted among the thinkers who made liberalism possible. And we may yet be riveted by Markus’ notion that our concept of the ‘secular’, so ubiquitous in modern life, first appeared in perhaps the least likely of places, in a momentary flash at the end of antiquity.