From 1877 until his death, he worked with archaeologists such as Heinrich Schliemann, Arthur Evans and Georg Karo, drawing and restoring ancient objects from sites such as the Acropolis of Athens, Mycenae, Tiryns and Knossos.

[14] George's younger son Nicholas enjoyed the lessons and looked back on Gilliéron with fondness, and his older brother, the future king Constantine, later served as the president of the Archaeological Society of Athens.

[24] His close association with the Institute continued throughout his career: among the German archaeologists with whom he collaborated were Wilhelm Dörpfeld, Ernst Fabricius, Adolf Furtwängler, Paul Hartwig, Georg Karo, Gerhard Rodenwaldt, Theodor Wiegand, and Franz Winter.

[27] Many of his reproductions of vase paintings appeared after his death in the publication by the German Archaeological Institute of the ceramic finds from the Acropolis, which used his drawings when photographs alone were inadequate to illustrate the decoration of the vessels.

[31] After Robinson moved to the Metropolitan Museum of Art in New York in 1906, that institution too purchased hundreds of paintings, replicas, and other objects from Gilliéron and his son, including watercolours of the architectural sculpture from the Acropolis.

[38] His work as a draughtsman was not confined to antiquities: in 1880 he accompanied Spyridon Lambros to Mount Athos in order to make copies of the frescoes of the Byzantine painter Manuel Panselinos in the church of Protaton at Karyes,[39] and at some point before 1885 he was hired by the Marquess of Bute to copy the poorly preserved Christian frescoes in the Parthenon and the church of the Megale Panagia in Athens, as well as other paintings at Mistra in Laconia.

Robert had received a donation from Halle banker Heinrich Franz Lehmann [de] to fund the work, and had been referred to Gilliéron by their mutual friend Paul Wolters.

[41] Gilliéron made two trips to Italy: during the first, in 1893, he produced watercolor copies of six ancient paintings on marble panels in the National Archaeological Museum in Naples, five of which had been found at Herculaneum and one at Pompeii.

According to Wolters, Gilliéron was as interested in the technical problems as he was in the artistic ones, and in the case of damaged originals his reproductions went beyond mere copies by reuniting broken fragments and restoring missing pieces.

[50] Gilliéron reproduced the cups with the assistance of the Swiss metalworker Jules Georges Hantz, director of the Musée des arts décoratifs in Geneva, first in 1894 for Salomon Reinach, the curator of the French National Archaeological Museum, and subsequently for other customers as well.

An illustrated catalogue of the objects for sale was published in German, French, and English, with an introduction by Wolters, which described the original artefacts in detail and vouched for the accuracy of the reproductions.

25 March), included depictions of the Nike of Paionios and the so-called Hermes of Praxiteles, two works of sculpture recently discovered in the excavations at ancient Olympia, as well as a statue of a discus thrower traditionally attributed to the Greek sculptor Myron.

A scene of wrestlers, for example, was taken from an Athenian red-figure krater depicting the legendary wrestling match between Heracles and Antaeus, while a stamp with a figure of a discus thrower and a tripod reproduced the device on a coin from the island of Kos.

[65] A series of circular plaster reliefs in the Gilliéron archive at the French School at Athens depict events in the pentathlon and seem to have been models for the decoration of proposed trophy cups; these, like the postage stamps, were based on ancient vase paintings and other works of art.

[71] In 1907 Gilliéron was chosen by the Archaeological Society of Athens to produce watercolor copies of the painted funerary stelai from the Hellenistic city of Demetrias (Pagasai) in Thessaly.

In the Society's excavations at the site, directed by Apostolos Arvanitopoulos [el], more than 700 tombstones of the 3rd and 2nd centuries BCE, many with their polychrome decoration still well preserved, were found reused as building material in the fortifications of the city.

[72] Their importance was immediately recognized: a new museum to house the finds was built in Volos, a program of conservation was begun, and Gilliéron was hired to make copies of some of the best preserved stelai in order to document their coloring while it was still fresh.

[77] Gilliéron père was hired between 1910 and 1912 by the German team, led by Georg Karo, continuing Schliemann's excavations at Tiryns; he restored the so-called "Shield Frieze" fresco from over two hundred fragments found in the inner forecourt of the palace.

Gilliéron fils has been credited by the archaeological historian Joan Mertens with improving the commercial success of their joint studio, and with extending its clientele to include patrons in Cuba and the United States as well as in Europe.

[84] His youngest brother, Jules Gilliéron, became a linguist at the École pratique des hautes études and co-authored the Atlas linguistique de la France.

[88] Mertens has written that Gilliéron's significance lay partly in being present at the unearthing of so many major archaeological discoveries, and being able to record their original colours before exposure to light and air damaged them.

[90] Gilliéron's contemporaries praised his skill as a draughtsman, particularly the precision with which he reproduced the finest details of the works that copied, and his ability to recognize faint traces of original decoration on badly damaged artifacts.

Of the archaeological problems of restoration he had a complete understanding; above all, he was the most helpful assistant in recovering and clarifying almost-vanished traces on severely destroyed originals, and he always made every effort to interpret them correctly.

The purely artistic qualities of his watercolors have been admired more recently as well: Mertens describes the paintings of Acropolis sculpture in the collection of the Metropolitan Museum in New York as "tours de force of the watercolorist's art", and praises "his mastery of the media, both in the pencil drawing and in the application of color.

Even with the use of technical aids to reproduce existing models or templates, the fluency of his execution over such large surfaces is exceptional, and, whether totally accurate or not, his sense of color in many areas is ravishing.

"[93] Wolters similarly observed that "he demanded sharp criticism from us and expressed open displeasure if a drawing was accepted sight unseen", because this suggested to him that the client did not take the work as seriously as he did.

[94] The Gilliérons' prominent role in the reconstruction and publication of many of the most high-profile archaeological finds of their lifetime has led Mertens to conclude that "their images, in large measure, have defined our visual impressions of the great ancient cultures of the Greek world".

[96] When the English writer Evelyn Waugh visited Knossos in 1929, he wrote that it was impossible to gain an appreciation of Minoan painting there, since original fragments of fresco were crowded out by modern restorations, and judged that Evans and Gilliéron had "tempered their zeal for reconstruction with a predilection for the covers of Vogue".

[100]Referring to the Gilliérons' practice of combining fragments later evaluated to have come from discrete images, a modern study has concluded that they "created a decorative programme which, as it currently stands, never existed".

[108] The archaeologist Leonard Woolley, who visited Crete in 1923–1924, was present at a police raid on a workshop where local Cretan craftsmen produced forgeries of Minoan snake goddess figurines, and wrote that the forgers were working for Gilliéron.