Most of his works are illustrated from sketches made by himself, which have been praised for their exactness and minuteness, though they do not show any exceptional artistic power. In 1801 he visited the Troad, where he made numerous sketches and fixed the site of Troy at Bounabashi (Schliemann, Ilios, p. 186). He published the ‘Topography of Troy’ in 1804, folio, a work to which Byron alludes in his ‘English Bards’ (first ed. 1809):
Of Dardan tours let dilettanti tell,
I leave topography to classic Gell.
While the ‘English Bards’ was printing Byron became acquainted with Gell, and altered the ‘coxcomb Gell’ of his manuscript to ‘classic Gell.’ In the fifth edition Byron, having then himself visited the Troad, altered ‘classic’ to ‘rapid,’ with the note: ‘“Rapid” indeed! He topographised and typographised king Priam's dominions in three days’ (Byron, Works; Moore, Life of Byron, 1 vol. ed. 1846, p. 76). On 14 May 1803 Gell was knighted on returning from a mission to the Ionian Islands. In 1804 he began a journey in the Morea, and left it in the spring of 1806 to visit Ithaca in company with Edward Dodwell, the traveller [q. v.] He afterwards published the ‘Geography and Antiquities of Ithaca,’ London, 1807, 4to; the ‘Itinerary of Greece,’ London, 1810, 4to (compiled 1801–1806), new edition, London, 1827, with a hundred routes in Attica, Bœotia, Phocis, Locris, and Thessaly; ‘Itinerary of the Morea,’ London, 1817, 8vo; and ‘Narrative of a Journey in the Morea,’ London, 1823, 8vo, in which he says (p. 306), ‘I was once very enthusiastic in the cause of Greece; [but] it is only by knowing well the nation that my opinion is changed.’ Byron wrote an elaborate article (reprinted in Moore, Life of Byron, Appendix) on the ‘Ithaca’ and ‘Itinerary of Greece’ in the ‘Monthly Review’ for August 1811. Gell does not appear to have been a collector of antiquities, and his writings on Greece have a topographical rather than an archæological interest.
In 1814 when Princess (afterwards Queen) Caroline left England for Italy, Gell accompanied her as one of her chamberlains. He gave evidence on 6 Oct. 1820 at her trial before the House of Lords, and stated that he had left her service merely on account of a fit of the gout, and had seen no impropriety between her and the courier Bergami (Hansard, Parl. Debates). Gell, however, in his letters of 1815 and 1816, written under such signatures as ‘Blue Beard,’ ‘Adonis,’ ‘Gellius (Aulus),’ retails little bits of scandal about the queen. He had sixty or seventy letters of hers in his possession. ‘What curious things they are!’ he says. From 1820 till his death Gell resided in Italy. He had a small house with a pleasant garden at Rome, and painted (1828) his sitting-room ‘in all the bright staring colours I could get, a sort of thing between Etruscan and Pompeii.’ At Rome he went much into society. He had another house at Naples, where, ‘surrounded by books, drawings, and maps, with a guitar, and two or three dogs,’ he received a constant stream of distinguished visitors. At Naples he was especially intimate with Sir William Drummond, the Hon. Keppel Craven [see Craven, Keppel Richard], and with Lady Blessington (from 1824), whom he visited at the Villa Belvidere, and to whom he addressed many lively letters (printed in Madden, Countess of Blessington, ii. 22–97; see also Gell's letters, ib. 488–500). When Sir Walter Scott visited Naples he saw more of Gell (between 5 Jan. and 10 May 1832) than of any English resident there. Gell, though greatly crippled, showed Scott the objects of interest near Naples, took him to Cumæ and (9 Feb. 1832) to Pompeii, where they dined ‘at a large table spread in the Forum.’ After Scott's death Gell drew up an account of their intercourse at Naples, part of which is printed in Lockhart's ‘Life of Scott,’ chap. lxxxii. It was to Gell that Scott made the well-known remark that Byron ‘bet’ (beat) him in poetry. From about 1815 till his death Gell suffered severely from gout and rheumatism, but he was always cheerful, and at this period did some of his best known archæological work. Between 1817 and 1819 he published, aided by J. P. Gandy [see Deering, John Peter], his ‘Pompeiana: the Topography, Edifices, &c.,’ London, 8vo. In 1832 he published (alone) ‘Pompeiana: the Topography, Ornaments,’ &c. 2 vols., London, 4to, giving the results of the Pompeian excavations since 1819. These books were well received in England and on the continent. Gell had obtained from the government special facilities for visiting the excavations and made very numerous sketches (reproduced in the volumes) of objects which he declares would otherwise have perished unrecorded. In 1834 he published the ‘Topography of Rome and its Vicinity,’ 2 vols., London, 8vo (2nd edition by E. B. Bunbury, 1826; cf. A. Nibby, Le Mura di Roma, 1820, 8vo, and his Analisi, &c., 1837, 8vo). To this work the Society of Dilettanti, of which Gell had become a member in 1807, contributed 200l. Gell was ‘resident plenipotentiary’ of the society in Italy, and regularly forwarded reports