A much more notable and better publicized use of iron followed shortly after this when metal replaced masonry for the entire central structure of the Coalbrookdale Bridge in Shropshire. This was begun in 1777 by Thomas Farnolls Pritchard (?-1777) with the active co-operation of Abraham Darby III, an important local ironmaster.[149] Darby’s Coalbrookdale Foundry cast the iron elements that were needed and the bridge was completed in 1779. Pritchard was an architect, and architects played a more important part in the story of the early development of iron construction than is generally realized. Soon, however, the importance of special problems of statics to which such construction gave rise and, above all, the need to measure accurately the strength of various components required the expert assistance of civil engineers, and often the engineers came to build on their own without the collaboration of architects. At this point the story crosses the channel to France.[150] There Soufflot, the very technically minded architect of the Paris Panthéon—one of the edifices with an account of which this book began—assisted by his pupil Brébion, provided in 1779-81 an iron roof over the stair-hall[151] that he built to lead up to the Grande Galerie of the Louvre. In the next few years two rather obscure French architects, Ango and Eustache Saint-Fart (1746-1822), were occupied, respectively, with the introduction of iron framing and of ‘flower-pot’ (i.e. hollow-tile) elements supported on timber framework to produce more or less fireproof types of floors. Over the years 1786-90 the great French theatre architect J.-V. Louis (1731-1800), horrified by the recurrent fires at the Palais Royal, combined these two ideas when he designed the roof of the new Théâtre Français in Paris. Now the main line of advance returns to England. In 1792-4 Soane avoided timber altogether in the fireproof vaults of his Consols Office at the Bank of England, using nothing but specially made earthenware pots; he also covered the twenty-foot oculus in the central vault with a lantern of iron and glass (Plate 3). The architectural qualities of this interior have already been stressed. Even more important for later architecture, however, although effectively invisible, had been the adoption just before this of French principles in a calico mill at Derby and the West Mill at Belper, both begun in 1792. These were planned and carried out by the millowner-engineer William Strutt (1756-1830) who used specially designed iron stanchions throughout carrying timber beams and, in the top storey only, ‘flower-pot’ vaults between the beams such as Saint-Fart had first introduced, but flat brick vaults or ‘jack-arches’ elsewhere.