In 15th-century Siena, two artists appear above all to have supplied the popular demand for devotional images: Sano di Pietro and Giovanni di Paolo. The list of extant works by both these painters is of truly astonishing length and increases constantly. But while the work of Sano di Pietro, with a few exceptions, scarcely rises above the level of soulless and mechanical craftsmanship, it may be said that there is no work of Giovanni di Paolo's which does not possess a real charm. He is assuredly not a great artist; but his emotion is quite vivid and sincere, and expressed with a directness which cannot leave one indifferent.  The picture of SS. Fabian and Sebastian, now for the first time reproduced by kind permission of its owner, Mr. Robert Ross, has so far not found a place in the published lists of Giovannidi Paolo's works. To those familiar with the style of this painter his name must suggest itself at once before this panel: these types and peculiarities of drawing, this technique and scheme of colour are so characteristically Giovanni di Paolo's and nobody else's. For delicate drawing and exquisite silhouetting, the figure of S. Sebastian- shown in the triumphant attitude constantly adopted in Sienese quattrocento painting, without the introduction of a column or tree-trunk favoured in realistic Florence-has scarcely its superior in the whole of Giovanni di Paolo's work. How characteristic of the Gothic generally is the design of the nude- one's thought goes inevitably to some of the figures in the miniatures of the Limbourgs- and yet how clearly the personal note makes itself felt in the rhythm of line.  The panel is on the whole in excellent preservation, and the harmony of the pale greenish-pink flesh tones, the white and the gold- all luminous tones contrasting with the deep mulberry of the Pope's dalmatic- is most fascinating.  The history of the panel cannot be traced very far back; it was acquired by the present owner from the late Mr. Charles Butler's collection sold at Christie's on the 25th and 26th of May, 1911 (No. 138, correctly named "Giovannidel Poggio"). The identification of the canonized Pope as S. Fabian rests on the fact that the feast of that saint occurs on the same day (Jan. 20th) as that of S. Sebastian. At the foot of the panel are represented, on a much smaller scale, two brethren of the Misericordia, kneeling with their hands joined in prayer and with a collecting spoon hanging from the wrist of each. Clearly this picture must have been painted for the altar of the chapel of some charitable brotherhood dedicated to SS. Fabian and Sebastian, and from the fact that the two brethren are affronted it seems likely that this was the principal, if not the only, panel of the altar-piece in question. To trace the original provenance of Sienese altar-pieces of this type is rather difficult- Siena had no Vasari of its own; and even had such a chronicler existed, in face of an activity like that of Giovanni di Paolo he would probably have had to conclude his account with the statement that the artist did infinite altre cose.