Henry James wrote of Venice: ''You desire to embrace it, to caress it, to possess it . . .'' whereas Mark Twain found St Mark''s ''so ugly . . . propped on its long row of thick-legged columns, its back knobbed with domes, it seems like a vast, warty bug taking a meditative walk''. Reactions to Venice have been, throughout the ages, astonishingly different. John Julius Norwich has put together a dazzling anthology, drawing on the writings of Byron, Goethe, Wagner, Casanova, Jan Morris, Robert Browning and Horace Walpole, among many others. The pieces range from the sixth century, when the early lagoon-dwellers lived ''like sea-birds in huts, built on heaps of osiers'' to the exquisite city of eighteenth-century revellers and nineteenth-century art lovers. The city''s many diferent guises are shown as both its citizens and visitors saw them. This wonderful volume from the Traveller''s Reader series also contains maps, engravings and notes on history, art, architecture and everyday city life.