Coal-tax posts are boundary marker posts found in southern England. They were erected in the 1860s and form an irregular loop between 12 and 18 miles from London to mark the points where taxes on coal were due to the Corporation of London. There were originally around 280 posts of which around 210 remain. History Coal imported into the City of London had been taxed since medieval times and, as it was originally all brought by sea to riverside wharfs, the collection of the duties was relatively easy. The City is a small (one square mile) but influential and rich part of London. The Port of London, within which the duties were payable, stretched far beyond the boundaries of the City, all the way along the Thames from Yantlet Creek (downstream from Gravesend) to Staines. By the 19th century, however, there was increasing trade by canal and rail, and various Acts of Parliament extended the catchment area to include these new modes of transport. In 1845 the boundary was set at a radius of 20 miles from the General Post Office, London, from Langley in the west to Gravesend in the east and from Ware in the north to Redhill in the south. In 1851 an Act permitted the erection of boundary markers to indicate where this boundary lay; and about fifty markers, inscribed with a reference to the Act, were erected. In 1861 a further Act – the London Coal and Wine Duties Continuance Act 1861 – was passed, reducing the area to that of the Metropolitan Police District plus the City of London. This stretched from Colnbrook in the west to Crayford Ness, at the mouth of the River Darent, in the east, and from Wormley, Hertfordshire, in the north to Banstead Heath, Surrey, in the south. New marker posts (about 280) were erected to show the boundary within which the duty was payable. These again cite the Act by regnal year and chapter number, i.e. 24 & 25 VICT CAP 42. In some cases, notably on railways and canals, markers made for earlier acts were reused on the new boundary. Most (over 200) of these posts survive. Although the title of the Act refers to wine duties, these were collected only in the Port of London: the boundary marks have no connection with the wine duties and it is incorrect to call them "coal and wine duty