Closely associated with the development of iron construction is the development of prefabrication; indeed, the parts of an elaborate iron edifice, such as a bridge or a greenhouse, are necessarily prefabricated and merely assembled at the site. From the early forties, and perhaps even before that, lighthouses were frequently erected in ironmasters’ yards in Britain, disassembled, shipped to Bermuda or the Barbadoes, and then reassembled. In 1843 John Walker of London provided a prefabricated palace for an African king and, by the end of the decade, prefabricated warehouses and dwellings of iron were being supplied to gold-diggers in California and emigrants to Australia in very considerable quantity. A look at the prefabricated houses of the 1940s will perhaps explain why almost none of these ancestors of a century earlier seems to have survived, at least in recognizable form. None the less, the advance of prefabrication remains a notable technical—though hardly architectural—achievement of the 1840s and 1850s. To the mid and late forties belong several splendid examples of mixed construction in various countries that not only represent technical feats of a high order but are also fully architectural in character. Some are by architects, others by teams of architects and engineers working in close collaboration. In building the Britannia Bridge,[167] which crosses the Menai Strait near Telford’s Menai Bridge, the Derby Trijunct team of Stephenson and Thompson in 1845-50 utilized with great success the rectangular tubes built up of wrought-iron plates that Fairbairn, the consulting engineer, recommended (Plate 61). The Holyhead railway line still passes through these tubes. The masonry entrances and the tall towers, taller than they need have been because of Stephenson’s original intention to use suspensory members for additional support to his rigid tubes, were superbly detailed by Thompson. Contemporaries called them Egyptian, but the design has already been noted as fully consonant with Romantic Classicism though quite devoid of Grecian elements. At least the sculptor John Thomas’s pairs of gigantic lions at the entrances are Nubian! At the London Coal Exchange[168] built in 1846-9 in Lower Thames Street, the City Corporation’s architect Bunning arrived at no such complete co-ordination of masonry and metallic design as did Stephenson and Thompson on the Britannia Bridge. The masonry exterior consists of two _palazzo_ blocks set at a fairly sharp angle to one another and loosely linked by a very Picturesque round tower, free-standing in its upper stages. Behind all this the dome of the interior court can barely be glimpsed. Inside this court, however, no masonry at all is visible; one sees only an elegant cage of iron elements rising to the glazed hemisphere above (Plate 63). The metal members are richly but appropriately detailed, and there is even more appropriate decorative painting by Sang in such panels as are not glazed.