Why these small marks matter

Britain's rivers and canals are covered in small, easily missed pieces of history. A painted number on a bridge abutment, a weathered stone post on a towpath, a rusted iron plate bolted to a lock gate — these were once essential pieces of working infrastructure. They told bargees how far they had come, how much they owed in tolls, where a ferry would take them across, and how deep the water ran. Most date from the great age of river improvement between roughly 1650 and 1900, when Parliament created dozens of navigation authorities to make rivers passable and profitable.

Today they are historical evidence. A toll board can show exactly what a cargo of coal cost to move in 1790. A ferry marker can pin down a crossing that appears on no modern map. A carved depth gauge can reveal how a channel has shifted. Very little of this is formally recorded, and much of it is quietly rotting away.

Painted numbers: tolls, arches and water levels

Numbers are the commonest form of marker, and the hardest to interpret without context. On a stone bridge, they usually run in sequence across the arches — arch 1, arch 2, arch 3 — so that a boatman knew which span to aim for in high water. Where the numbers are irregular, or appear only on one side, they may instead record river miles from a defined starting point, such as a town bridge or the head of navigation.

Look also at the vertical scales painted on lock cottages, weir walls and bridge piers. These are flood and depth gauges, sometimes with the highest recorded flood level cut in as a permanent line. Useful details to note:

• Whether the number is painted directly onto stone, carved, or on a separate plate.
• The colour scheme — many authorities used standard liveries, and repainting often overpaints older lettering.
• Any faint earlier numbers beneath the current ones, visible in raking light.
• Whether the sequence continues on the opposite bank or a nearby structure.

Stone posts, ferry stances and boundary stones

Short stone posts along a towpath or riverbank usually mark one of three things: a parish or county boundary, a ferry landing point, or the limit of a navigation authority's jurisdiction. Ferry posts often survive as a pair, one on each bank, sometimes with an iron ring for the rope or chain. The word "ferry" may be cut into the face, or the post may carry only initials and a date.

Boundary stones tend to be squarer and more deeply inscribed, often with two sets of initials back to back. They matter because they frequently preserve the names of parishes that were merged or renamed in the twentieth century. Where a stone sits beside a weir, a mill leat or an old wharf, it is worth checking whether it records a milling or fishing right rather than a parish line.

Iron plaques, mileposts and lock furniture

Cast iron was the Victorian answer to durable signage, and it has survived remarkably well. Mileposts along navigations such as the Thames, the Severn and the Great Ouse typically give the distance to a named town in miles and furlongs, with the maker's name and a date cast into the base. Lock gates, paddle gear and sluice frames often carry small oval or rectangular plates bearing a number, an authority name, or an instruction.

Two cautions apply. First, iron plates are stolen, so record them promptly and note their condition. Second, many plates have been moved, sometimes during restoration work and sometimes by souvenir hunters, so a plate's present position is not proof of its original one.

Photographing a marker so it is actually useful

A single close-up of a weathered inscription is nearly useless on its own. Take a set of four or five frames instead:

• A wide shot showing the marker in its landscape, with the river or towpath visible.
• A medium shot from about two metres, filling the frame with the object.
• A tight shot of any inscription, lit from the side to bring out the lettering.
• A shot with a scale — a coin, a notebook or a tape — laid beside the text.
• A shot looking along the bank in both directions, which helps later map-matching.

Photograph in flat, overcast light where you can. Direct sun washes out shallow carving, and flash flattens painted lettering badly.

Grid references, notes and where to send them

Record an OS grid reference to at least eight figures, taken standing at the marker rather than from the car park. Note the date, the river or canal name, the nearest bridge or lock, the water level, and the weather if it affects legibility. Write down anything you cannot photograph: the smell of a decaying timber post, a fresh coat of paint, a broken corner.

Then pass it on. County historic environment records, local records offices and the relevant navigation authority all welcome well-documented finds, and a dated photograph with a precise grid reference is exactly what they need. If the marker is on private land, record it from the towpath or a public footpath and do not climb fences. Never lever a plate off a wall or scrub a stone clean — you will destroy more than you reveal. The value of these marks lies in their position and their patina, so leave them exactly where they are and let your notes do the work.