The name of Holborn was formerly derived from Old Bourne, a tributary of the Fleet, the valley of which is clearly seen where Holborn Viaduct crosses Farringdon Street. Of the existence of this tributary, however, there is no evidence, and the origin of the name is found in _Hole-bourne_, the stream in the hollow, in allusion to the Fleet itself. The fall and rise of the road across the valley before the construction of the viaduct (1869) was abrupt and inconvenient. In earlier times a bridge here crossed the Fleet, leading from Newgate, while a quarter of a mile west of the viaduct is the site of Holborn Bars, at the entrance to the City, where tolls were levied. The better residential district of Holborn, which extends northward to Euston Road in the borough of St Pancras, is mainly within the parish of St George, Bloomsbury. The name of Bloomsbury is commonly derived from William Blemund, a lord of the manor in the 15th century. A dyke called Blemund's Ditch, of unknown origin, bounded it on the south, where the land was marshy. During the 18th century Bloomsbury was a fashionable and wealthy residential quarter. The reputation of the district immediately to the south, embraced in the parish of St Giles in the Fields, was far different. From the 17th century until modern times this was notorious as a home of crime and poverty. Here occurred some of the earliest cases of the plague which spread over London in 1664-1665. The opening of the thoroughfares of New Oxford Street (1840) and Shaftesbury Avenue (1855) by no means wholly destroyed the character of the district. The circus of Seven Dials, east of Shaftesbury Avenue, affords a typical name in connexion with the lowest aspect of life in London. A similar notoriety attached to Saffron Hill on the eastern confines of the borough. By a singular contrast, the neighbouring thoroughfare of Hatton Garden, leading north from Holborn Circus, is a centre of the diamond trade.