In the spring of 1900, Philip de László was granted a rare audience (and portrait commission) with Pope Leo XIII (1810-1903). The aged pontiff received him with a gentle gaze and a mind still sharp from decades of theological and diplomatic engagement. A recent Catholic convert, de László sought to capture the essence of the Pope’s spiritual authority. ‘I can say that I have never met a man whose innermost feelings were revealed so expressively,’ he later wrote. Yet his first portrait was met with disapproval; Leo felt it bore an unfortunate resemblance to Voltaire, whose influence he regarded as morally corrosive. Undeterred, de László painted a second version, avoiding all secular allusions. The approved likeness now hangs in the Hungarian National Gallery in Budapest.

The world has rediscovered Leo XIII with the election of his namesake successor, Leo XIV. The internet buzzed with curiosity, sparked by a grainy black-and-white clip of the elderly pontiff bestowing a blessing before the camera – believed to be the earliest-born person ever captured on film. One of the longest-serving popes and the oldest to die in office, Leo XIII presided over an intellectually and spiritually ambitious papacy that helped steer the Catholic Church from the 19th century into the 20th.

Leo XIII was born nearly a century before his portrait was painted. On 2 March 1810, in the hill town of Carpineto, nestled between two limestone spurs of the Monti Lepini south of Rome, Gioacchino Vincenzo Raffaele Lodovico Pecci entered the world. The fourth of six children, he was born into the sturdy grandeur of a 15th-century palazzo overlooking the Volscian plain. His father, Count Domenico Pecci, came from old Sienese stock; the family had settled in the Papal States under the patronage of Pope Clement VII. His mother, Anna Prosperi-Buzi, was remembered by her son as ‘most devoted to the poor, always working for them’.

While Gioacchino grew up among the serene, olive-covered slopes of Latium, the wider world was in convulsion. Pius VII had been seized by Napoleon and shuttled from prison to prison across France. His return to Rome after Waterloo restored the dignity of the Holy See, and one of his first acts was to re-establish the Society of Jesus. Count Pecci entrusted his two youngest sons, Giuseppe and Gioacchino – then ten and eight – to the newly founded Jesuit college in Viterbo, where the latter displayed a precocious gift for Latin, delighting especially in the orators and poets of classical antiquity.

In 1824, the new Pope, Leo XII, restored the Collegio Romano to the Jesuits. The following year, over 1,400 students enrolled, among them Gioacchino Pecci. As in Viterbo, his studies included rhetoric, Latin and Greek composition, and classical history, though he also excelled in the sciences, winning prizes in physics and chemistry. His contemporaries recalled his singular discipline and quiet nature: the whole time he lived at the Palazzo Muti with his uncle, Antonio, Gioacchino shunned diversions, avoided society, and abstained even from games. In the Jubilee of 1825, Pecci was chosen to lead a student deputation to the Pope and deliver an address of thanks, a moment deeply etched in his memory, and an impression that later shaped his choice of papal name.

By 1830, as Rome entered an Indian summer of spiritual and intellectual renewal, Pecci enrolled at the Gregorian University. Resolving to enter public service under the papal government, he later studied at La Sapienza, where he pursued both civil and ecclesiastical jurisprudence, along with advanced theology and sacred doctrine. Years of rigorous study culminated in a doctorate in both civil and canon law, qualifying him for a career in the Church’s higher administration. Soon noticed by figures in the Roman Curia, he was recommended to Pope Gregory XVI. In January 1837, Pecci was appointed Domestic Prelate and joined various papal administrative bodies, and, in November, he received the sub-diaconate and diaconate from the Pope’s Vicar General; on the last day of the year, Pecci was received into Holy Orders.

Between 1838 and 1843, Monsignor Pecci administered a series of communes across the Papal States with distinction. His first appointment, in February 1838, was as Governor of Benevento, a tiny papal enclave of just 46 square miles, once held by Talleyrand, who had been created Prince of Benevento by Napoleon. French occupation and the rise of Carbonarism had left the region politically volatile and morally unsettled; brigandage was rife, and papal and Neapolitan authority alike was widely disregarded. Pecci quickly revealed the traits that would define his later career: decisiveness, moderation, and a mind at once practical and intellectual. Within three years he had eradicated brigandage, expelled agitators, and revived local agriculture and industry.

His success led Rome to entrust him with the larger and more turbulent province of Spoleto, and soon after, with Perugia, long a centre of civic unrest. There, he brought the same blend of administrative rigour and reforming zeal. Within just 20 days of his arrival, he had overseen the construction of a broad, paved thoroughfare, the Strada Gregoriana, up the hillside, enabling a ceremonial papal entry and symbolising a new spirit of civic openness. Drawing on his Vatican experience, he reorganised municipal councils, unified the courts into a central tribunal, and cleared a backlog of legal disputes. Moreover, he founded the Perugia Savings Bank to promote thrift among labourers and extend credit to artisans and farmers, contributing personally to its capitalisation.

Yet Pecci was no mere lay administrator. A scholar himself, he held that Italy’s regeneration required a class of educated and religiously grounded leaders, from whose renewal enlightenment might descend. He pursued this aim by revitalising the College Rosi in Spello and working closely with religious orders to strengthen popular education. Before long, Gregory XVI recalled him to Rome. A new, delicate diplomatic assignment awaited: the leadership of the Holy See’s mission to the new Kingdom of Belgium.

Indeed, in January 1843, Gioacchino Pecci was made titular Archbishop of Damietta and appointed Apostolic Nuncio to the court of Brussels. Belgium, which had seceded from the Netherlands in 1830 under the protection of the Great Powers, did so largely in pursuit of religious liberty for its six million-strong Catholic population. In the years that followed, the young kingdom emerged as a haven for political exiles, secret societies, socialists, and anarchists, who wrote, published, and plotted against the monarchies of the Continent. On the other hand, the Belgian clergy, staunch defenders of denominational education, resisted all efforts to impose a secular school system.

In late March, Archbishop Pecci presented his credentials to King Leopold I of Saxe-Coburg, a liberal-minded, nominally Protestant monarch, who sought to curtail Catholic educational dominance and was uncle to Queen Victoria and Prince Albert. Pecci made an immediately favourable impression at court. His erudition, genteel upbringing, courteous manner, and engaging conversation were quickly recognised by the royal couple. A Belgian biographer later observed: ‘The affability of Monsignor Pecci, his exquisite tact, and his deep learning forced Leopold I to form a very high opinion of him.’ The king often remarked: ‘Really, Monsignor, you are as clever a politician as you are an excellent churchman.’

Queen Louise, at the counsel of Pecci, worked to uphold the liberties of conscience and worship promised to Catholic Belgians under the new constitution. The Nuncio aligned himself with the clergy and bishops, revealing a conservative bent in his character by vigorously supporting the cause of denominational schools. He also played a leading role in establishing the Belgian College in Rome, which endures to this day.

By the autumn of 1845, Pope Gregory XVI was persuaded to once again recall Pecci to Italy and appoint him Bishop of Perugia. Before his departure, King Leopold invested him with the Grand Cross of the Order he had founded and wrote personally to the Pope: ‘I feel bound to recommend Archbishop Pecci to the kind protection of Your Holiness: he deserves it in every respect, for I have seldom seen a more uncommon devotion to duty.’

Yet when Pecci delivered the letter in Rome two months later, the Pope lay on his deathbed and was unable to read it. The intervening weeks, which Pecci had spent in Paris and London – where he was presented to Queen Victoria – left a lasting imprint. Had he returned directly from Brussels, it is possible the dying Pope might have cancelled the Perugia appointment and named him a cardinal instead. Though intended as a reward, the transfer removed from diplomacy a young man of rare ability, consigning him to over 30 years of relative obscurity in a provincial bishopric. The move would prove unfortunate not only for the future pope, but for the Vatican itself, as the storms of the Risorgimento were gathering above the Holy See.

Pecci’s 32-year tenure as Bishop – and later Archbishop – of Perugia was marked by quiet but resolute service, pastoral diligence, and a growing reputation for balancing theological conservatism with social engagement and Christian charity. He worked to raise the moral and educational standards of the clergy, championed the revival of Thomist philosophy, and consistently emphasised the Church’s civic role. His episcopacy unfolded amid profound political upheaval: the Risorgimento, the unification of Italy, the dismantling of the Papal States, and the capture of Rome by Italian forces in 1870. Pope Pius IX, originally a reformer, responded to these losses by entrenching doctrinal rigidity and retreating from political compromise, declaring himself a ‘prisoner in the Vatican’. By the time of his death in 1878, the Church was internally divided and externally diminished: a moral authority adrift in an increasingly secular Europe.

It was in this climate of crisis that the College of Cardinals convened. Pecci, appointed Camerlengo, who serves when there is no Pope, the previous year, emerged as a natural candidate. For the first time in over a century, the conclave was not held in the Quirinal Palace – now under Italian control – but in the Vatican’s Pauline Chapel. With the traditional Catholic powers absent, the cardinals were left free to choose the man they deemed most worthy to lead the Church. Sixty-four electors assembled, only four of whom had participated in the conclave of 1846. Pecci received 23 votes in the first ballot, 38 in the second (reportedly with tears in his eyes and hands trembling) and 44 in the third, securing his election. Pale and visibly shaken, he seemed almost ready to plead with the College not to choose him.

As he appeared on the balcony of St Peter’s Basilica, proclaimed to the crowd as Lumen in caelo, the new Pope’s pale, ascetic figure, his white hair catching the Roman light, his expression solemn, etched an image that lingered in many minds. It was an image later captured with uncanny fidelity by de László. So, from diplomat and provincial bishop to Supreme Pontiff, Pecci’s long journey had come full circle. His election marked the beginning of a papacy that would reshape Catholic engagement with modernity through diplomatic reorientation, doctrinal clarity, and a bold social vision.

Spurred by a sense of urgency and conviction, he authored 86 encyclicals. Yet several themes warrant closer attention because of their contemporary relevance: his social doctrine; his stance in the ‘culture wars’ of his time; his efforts to revive Aquinatic philosophy, and his forging of the Church’s social doctrine.

Leo XIII focused on the contemporary Kulturkampf over the meaning of civilisation. In an age of rapid industrial expansion, rising nationalism, and growing secularism, the Pope saw the rhetoric of progress and modernity not as morally neutral, but as instruments for marginalising the Church. Having witnessed the dismantling of the Papal States and the decline of papal temporal power, he viewed modern civilisation not as the triumph of reason and liberty, but as a contested space from which the Church was being deliberately excluded. He rejected the notion that Church and civilisation stood in ‘intrinsic repugnance and irreconcilable hostility’.

Rather, he argued, true civilisation was possible only where divine and natural law shaped the moral foundations of society. Some of Leo’s more reactionary instincts emerged most clearly in his denunciations of the zeitgeist: ‘The immoral press poisons souls; art, prostituting itself, defiles the senses with hideous figures; the theatre offends good taste and modesty; there are limits placed on churches and ministers of worship; usurers of liberty exact the most enormous interest; speculators realise the most dishonest gains.’ In all that, the Pope discerned a society in moral freefall and degeneracy and attempted to articulate the Church’s defence of religious tradition, aesthetic order, and moral clarity against the perceived chaos of modern secular life.

In his effort to reconcile Christianity with modernity, faith with reason, and religion with scientific progress, Leo XIII turned decisively to the teachings of St Thomas Aquinas. He regarded the ‘Angelic Doctor’ as the ideal guide for reasserting Catholic intellectual authority in a secularising age. ‘The method and doctrine of Aquinas’, Leo wrote, ‘must be the light of all higher teaching, for his works are but revealed truth set before the human mind in its most scientific form.’ In Aquinas, he found a system in which the natural and supernatural orders converged, where science and theology complemented rather than contradicted one another.

Far from rejecting modern currents of thought, Leo believed that authentic progress in the arts and sciences was not only compatible with, but enriched by, a Thomist framework. Yet he remained firm in his conviction that education must be rooted in explicitly Christian principles. In his 1879 encyclical Aeterni Patris, he declared that Thomistic philosophy should serve as the foundation of all Catholic teaching. Philosophy, he argued, must unite fidelity to faith with a rigorous respect for reason. The proper and scientific use of reason, Leo asserted, echoing the Church Fathers, and foreshadowing John Paul II and Benedict XVI, serves as a prelude to faith.

Aquinas had long been recognised as the architect of natural theology. His Summa Theologiae and Summa contra Gentiles exemplified order, rigour, and systematic reasoning. He held the classical authors in high veneration, synthesising Aristotle and Cicero with the Church Fathers and Augustine. The result was a philosophical edifice of enduring coherence. Leo’s revival of Thomism reinvigorated Catholic scholarship across Europe and beyond.

To institutionalise this revival, the Pope founded the Academy of St Thomas Aquinas in Rome and commissioned scholars to produce a critical edition of Aquinas’s works – the Editio Leonina. His vision found its most committed heir in his successor, St Pius X, who systematised and promoted Thomism as the Church’s official philosophical framework. Its influence reached far beyond seminaries. For example, in the United States during the Cold War, scholars such as Peter Stanlis and Francis Canavan drew on Thomist principles in their reinterpretations of conservatism, notably in relation to Edmund Burke.

For Leo XIII, the closing decades of the 19th century were marked by ‘marvellous discoveries in the natural sciences’ and the vast expansion of industrial pursuits. Nonetheless, this same period, he believed, had left the working man ‘isolated and helpless in the face of employers’ callousness and the greed of unchecked competition’. For many, life resembled little more than servitude. Disillusioned and in search of relief and justice, they turned to radical ideologies such as socialism and communism. ‘The condition of the working classes’, Leo wrote, ‘is the pressing question of the hour.’

Published in 1891, Rerum Novarum was Leo’s most forceful intervention in the moral dislocations of modern capitalism. While reaffirming the sanctity of private property, he condemned both the unregulated competition of liberal economics and the radical collectivism of socialism. ‘The main tenet of socialism, community of goods’, he declared, ‘must be utterly rejected’, not only as unjust, but as self-defeating. If no one could retain the fruits of their labour, what incentive remained for exertion, talent, or thrift? Socialism, he argued, would distort the role of the state, rob the lawful possessor, and plunge society into confusion and disorder.

Against the Marxist notion of class conflict, Leo reverted to a Thomistic vision of society as a moral organism: an interdependent whole whose parts were not locked in antagonism but bound by mutual obligations. He argued that ‘the rich and the poor are ordained by nature to live in harmony and agreement [so that] each class should make its own contribution to the common good’. This language, echoing the political thought of Cicero no less than the theology of Thomas, affirmed interdependence over struggle: capital could not do without labour, nor labour without capital. But where the classical tradition had stopped at civic harmony, Leo added a higher mediating principle: the Church, as moral authority, reminding each class of its duties and limits.

Thus, Rerum Novarum set forth, in striking detail, the obligations of both employers and workers. The former must never treat their employees as mere instruments of profit, but respect their human dignity, provide adequate rest, allow time for religion, family, and recreation, and never exact labour beyond one’s strength. The latter, in turn, must fulfil agreed work, preserve property, and refrain from violence or disorder. Yet beyond this juridical reciprocity, Leo invoked a deeper imperative: Christian charity, what Aquinas described as the principle by which one’s possessions, though legally one’s own, should be held as common when necessity demands. ‘Of what remains, give alms,’ Leo reminded his readers.

Among the wider ranging topics of the encyclical, Leo touched upon wages and the limits of free contracts. Where pay failed to sustain a decent and frugal life, Leo wrote, the worker was not truly free, but ‘the victim of force and injustice’. To this end, he endorsed Christian associations and trade unions, provided they remained voluntary, temperate in tone, and respectful of individual conscience and private property. These he saw as heirs to the medieval guilds, instruments of solidarity within the wider framework of the common good, while warning against coercion, partisanship, and subordination to radical politics.

A decade later, in Graves de Communi Re (1901), Leo returned to the theme to dispel lingering ambiguities. He explicitly rejected terms such as Christian Socialism and Social Democracy, preferring instead Christian Democracy – not in its constitutional sense, but as ‘beneficent Christian action on behalf of the people’. Such action, he insisted, aimed not at the overthrow of existing orders, but at the perfection of souls and the defence of justice by moral means: ‘[Christian Democracy and Social Democracy] differ from each other, as much as the sect of socialism differs from the profession of Christianity.’ This vision of principled reform continues to animate the centre-right on the Continent, in Germany and beyond.

Leo’s intervention did not arise ex nihilo. For example, in his final tract, Thoughts and Details on Scarcity, Burke, nominally Anglican, but essentially latitudinarian, contended that Christian charity should guide the relief of poverty, not the state. Burke’s political economy, unlike that of his friend Adam Smith, was suffused with theological concern. Catholic thinkers across Europe – Lamennais, Montalembert, and Lacordaire, to name just a few – grappled with the dislocations of industrial society, seeking to reconcile Church teaching with the emerging languages of rights and social responsibility. Later, Frédéric le Play and the Vicomte de Mun advanced a distinctively Catholic response to modern capitalism. What Leo achieved was not invention, but elevation, raising Catholic social thought to the level of magisterial doctrine.

Properly understood and disentangled from the polemics of party and ideology, the social doctrine Leo articulated offers a key to understanding many of the teachings and pronouncements of Pope Francis, especially on poverty and justice. It may also help us anticipate the initiatives and direction of the new pontificate whose bearer has, with symbolic deliberation, chosen the name Leo XIV.

In de László’s portrait, the pontiff’s gaze is distant yet resolute. It is the same face that flickers, briefly, in the earliest moving images of any pope: fragile, spectral, and strangely alive. In that grainy footage, as on the painter’s canvas, Leo XIII appears not as the relic of a vanished world, but as its final steward: serene in bearing, capacious in thought, and unshaken in the belief that even modernity might still be brought under the discipline of truth.