During his time in Italy he created his celebrated masterpiece L'Ecole de Platon (1898), which stands as a visual summary of his Idealist aesthetic which he promoted during the 1890s in his writings, poetry and exhibitions societies, notably the Salons d'Art Idéaliste.

At the start of his career, his esoteric perspective was mostly influenced by the work of Eliphas Levi, Edouard Schuré, Joséphin Péladan and Saint-Yves d'Alveydre, and later by the Theosophical writings of Helena Blavatsky and Annie Besant.

He was an astonishingly skilled draughtsman and painter capable of producing highly expressive works on a grand scale, many of which can be seen in public buildings in Brussels, including the Palais de Justice.

Delville's early efforts exhibited in 1887 were largely favourably reviewed in the contemporary press, notably L'Art Moderne and the Journal de Bruxelles, even if they were seen to be eclectic and derivative of the works of older established artists.

A contemporary review described it in the following: 'On a huge bed with purple sheets ... a dishevelled standing woman displays her nudity as she writhes in spasmodic movements, bending under the pains of childbirth.

Her face is contorted, her gnashing teeth alternate with the curse, her clenched hands lift the bed cover over her belly in an unconscious reflex of modesty ... abominable vision ....!

In an undated drawing titled Le las d’Aller Delville depicts a fallen figure curled up on his side in a barren landscape, asleep, or perhaps even dead.

Following Les XX, Pour L'Art invited international artists as well, several of whom became well known in Symbolist circles, including Carlos Schwabe, Alexandre Séon, Charles Filiger and Jan Verkade.

The leading critic Ernest Verlant wrote: One of the principal members of the Pour L'Art group, in view of his talent and astonishing fecundity, is Jean Delville, who is also a writer and a poet; with a powerful imagination that is funereal and tormented.

These epithets are equally suited to his large painting La Proie, a crimson vision of apocalyptic murder, similar to his vast composition from last year, Vers l’inconnu, and of several before that.

On the advice of his close friend, the sculptor Victor Rousseau, he was motivated to enter the prestigious Prix de Rome, which came with a very generous bursary that also covered the costs for a lengthy sojourn in Italy.

Competitors were isolated in small studios in the Academy of Fine Arts in Antwerp which ran the competition and were expected to produce a finished drawing of their composition before setting to work on the final painting.

Delville recorded his experience in his autobiography: The rules were demanding … At that time the six selected competitors for the final exam had to paint their work in a secluded lodge, after leaving the original preliminary drawing in a hallway of the Antwerp Academy.

The experience proved to be a turning point in his career and brought to focus his ideal to synthesise the classical tendency in art with his interest in esoteric philosophy which was the defining attribute of his Idealist aesthetic form then onwards.

These included his outstanding Orphée aux enfers (1896), a key initiatory work, as well as his great masterpiece of the period, his L'Ecole de Platon (1898), which he exhibited at the 1898 Salon d'Art Idéalist to universal praise.

The manifesto provides a valuable record of the Idealist movement founded by Delville: The intention of the Salons d’Art Idéaliste is to give rise to an aesthetic Renaissance in Belgium.

The show received largely positive reviews in the press and Delville's Salons were becoming more widely accepted, despite his aggressive polemics in the months prior to their establishment which hackled his contemporaries.

Among many other well-known Belgian artists represented are Albert Baertsoen, Jean Delville, Emile Claus, Herman Richir, Comte Jacques de Lalaing, and Paul Dubois.

Regarding this important aspect of his intellectual and spiritual life, he wrote in 1944: En réalité, la philosophie occulte occupe le fond de ma pensée depuis bien des années !

Je pense avoir lu à peu près tout ce qui fut publié d’important sur les problèmes de l’invisible.

[27] Delville outlines this in a vivid passage in his La Mission de l'Art where he emphasises the expressive value of Idealist art, in other words, that it is not merely a question of engaging passively with the image, but it is also about feeling the 'energy' that it radiates, which uplifts and transforms the consciousness of the viewer, in a spiritual way.

In his L'Ange des Splendeurs he captures the effect of iridescent, diaphanous gold in the angel's drapery contrasting distinctly with the heavy earthiness of the natural details (animals, spiders, vegetation) at bottom right hand side.

This is especially the case in the rendering of lithe and supple male and female figures in his Les Trésors de Sathan, L'Amour des Ames and L'Ecole de Platon, or the highly expressive drawn, sinewy, almost emaciated forms in the lower part of his epic l'Homme-Dieu displaying the suffering and distress of the human condition; or in the highly muscular, Titanesque rendering of anatomy in his heroic figures in his Prométhée and Les Dernières Idoles.

… Unfortunately, for the most part, we remain stubbornly ignorant of the fact that real virginity develops highly the powers of the soul, and that, to those who dedicate themselves to it, it imparts faculties unknown to the rest of the human race.

Oil on canvas, 260 x 605 cm, Paris: Musée D'Orsay In this important painting, Delville invokes the serene beauty of the Classical world and its aesthetic and philosophical principles.

The style of the painting is inspired by the Italian frescoes by Raphael and Michelangelo that Delville would have seen while in Rome, characterised by bold articuation of forms with a matte (as opposed to a glossy) finish.

This painting suggests a theme important to Delville and his contemporaries regarding the return to unity in the dual male and female principles of human experience that results in spiritual androgyny.

The role of modern idealism will be to draw the artistic temperament away from the deadly epidemics of materialism ... and finally to guide him towards the purified regions of an art that is the harbinger of future spirituality.

'[48] Delville remained desperately poor during the early part of his career and his condition was only occasionally relieved by the stipend associated with the Prix de Rome that he won as well as his employment at the Glasgow School of Art, and later the Ecole des beaux-arts.

Finally, Delville was fiercely independent in his approach to promoting his ideas and artistic ideals, seldom bending to the will of what was popular or acceptable in conservative bourgeois circles that controlled and dominated the art market during his formative years.