Twice a day the tides of the River Thames rise and fall, as all tides do, under the gravitational pull of the moon. The withdrawing tide sees the water level drop by as much as six or seven metres, revealing all manner of histories, from the remains of a Neolithic forest near Tilbury to Anglo-Saxon fish-traps at Chelsea. The deep, oxygen-free mud of the river’s foreshore lends itself to preservation, which means that at every low tide the tug of the waters might offer up almost anything from the ten millennia of human habitation beside it – things lost, things broken, things tossed away, things freely given to propitiate forgotten gods and spirits. The Thames is many things, but it is also a great and greedy hoarder of the city’s past, a liquid and capricious Oxyrhynchus.

The Secrets of the Thames, a fascinating new exhibition at the London Museum Docklands, which runs until 1 March 2026, explores both the discoveries that have been made on the foreshore, and those that go out at low tide, in search of trifles and treasures. Since at least the late 18th century, these have gone by the name of mudlarks, and the exhibition is bookended by two rooms that explore the practice of mudlarking itself.

These tell very different stories. The first focuses largely on the 19th century, when mudlarking was the preserve of the urban poor, if not the urban destitute. Henry Mayhew’s London Labour and the London Poor (1851) records that most mudlarks were children aged eight to 15, scavenging in the mud, feeling their way with feet and hands, for coal, rope, or scrap metal – anything they could use to earn enough for food and, perhaps, a bed for the night.

Contemporary mudlarking, meanwhile, is no longer concerned with the detritus of trade but with the material remains of Thames-side human cultures. For all that it now requires a permit from the Port of London Authority, it is primarily, if not exclusively, a leisure activity. The room dedicated to today’s mudlarkers features five large glossy photographic portraits of practitioners. The contrast with the poor and mostly anonymous Victorian women and children who foraged for the means to sustenance was striking. Much of the exhibition space is given over to social history; the social history of mudlarking itself might have been explored more thoroughly.

This is, to be clear, a minor criticism. Many of the artefacts are thematically displayed in cases set among a sequence of wittily imagined foreshores bursting with half-buried objects. One case offers gold rings, late medieval and early modern, inscribed with affirmations of love: pour amor say donne; mon cor avez; nul autre – that is, ‘for love I am given; have my heart; none other’. Each pulls at us, both in recognition of the shared human feeling and in the unrequited desire for the lost private history their presence in the river hints at.

This is, after all, the game the river plays with us. We are given glimpses into forgotten, anonymous lives made tenderly, haptically real again. Who was the Viking who lost their silver pendant of Thor’s hammer as they waited by the Thames for the spring tides? Who was Osmund, whose name is so carefully inscribed in silver on the iron seax – the knife which gave the Saxons their name – before losing it to the water some time before the end of the first millennium? Which poor 14th-century soul lost his long-toed shoe? Did he know whoever lost their superbly detailed leather belt?

Elsewhere, the brokenness of things somehow makes the maker almost as present as the artefact. Whose hands painted the bird from the early 17th-century fragment of delftware, whose thumbprint is pressed into the clay from the lining of an early 18th-century kiln? The mud has preserved a remarkable array of Roman artefacts: a vast Spanish amphora, figurines of both Roman and British gods, intaglios, building rubble. Again, the context of their preservation and the randomness of their recovery, their fragmentary nature, makes us look at them with more attention – and more imagination, too: we reach after the whole and arrive no closer than surmise.

Perhaps the most remarkable objects here are, in fact, more or less intact – and more or less immediately predate Roman London. One is a bronze horned helmet decorated with spare and delicate scrollwork that belies the belligerence of the overall piece: it is the only horned Iron Age helmet ever found in Europe. It emerged from the mud at Waterloo. The other astonishing find came from a little further upriver at Battersea. It is a large bronze shield, with three elaborate circular patterns – part engraved, part beaten – which seem to look forward in the elegance of their unfurling internal loops and curves to the shapes of Art Nouveau.

The last room is given over to one of Luke Jerram’s moon sculptures, the presence of which – lovely though it is – seemed to owe more to the need for an Instagrammable moment than any curatorial necessity. In some ways the choice seemed to reflect a lack of confidence in the content of the wider exhibition, which can’t always decide if it is about mudlarking itself or the artefacts uncovered during the fluvial game of hide and seek that the river plays with its keepsakes twice a day.

There are certainly some unarguably magnificent objects here, but some of them, at least, were not found as a result of mudlarking: the Waterloo helmet and the Battersea shield, for example, surfaced during the series of large-scale building works that went on beside the river in the 19th century. Rather than dedicating a room to the moon, perhaps, the exhibition might have given more space to how the working life of the river interacted both with mudlarking itself – the contents of those ships and barges from which Victorian and other mudlarks scavenged for their lives – and with the terrible labours that inadvertently brought so many artefacts to light. I wondered if the apparent curatorial discomfort with trade and exploration – seemingly synonymous with exploitation here – extended to the London people whose hard and meagre livelihoods were so dependent on such work.

I found myself thinking of Jesse Hexam’s trade in robbing the bodies of the river’s dead with which Dickens opens his 1864-65 novel Our Mutual Friend. The Thames is, among other things, the god of last resort for those most in need; for all that it has been tamed in recent centuries, it remains a wild place at the heart of urban civilisation, responsive to necessity, which is constant, and indifferent to morality, which is transient.

‘Everything I find is a fragment of something,’ the mudlarker Mark Sowden says in a video interview towards the end of the exhibition. And it’s true: even the most striking of the exhibits here – the Battersea shield, say, or Osmund’s seax, or a late-medieval eel spear – are no more than the fragments of a life, a culture, a moment in history, which the river has shored against our ruin. But if it has only ever offered up a few fugitive remnants of a limitless mosaic, those are still enough to provide sometimes moving, sometimes tantalising insights into the millions of human lives the great river has run through on its way to and from the wide salt estuary and the great and voluptuous indifference of a limitless world.