Dredging and embankment work along the Thames in the nineteenth and twentieth centuries produced an extraordinary quantity of metalwork: Bronze Age rapiers and spearheads, Iron Age daggers in decorated sheaths, and two of the finest pieces of Celtic art from Britain, the Battersea Shield and the Waterloo Helmet, both recovered from the river in central London. Human skulls have also come out of it in numbers, concentrated in particular reaches and with few other bones alongside them.
Richard Bradley's analysis of finds of this kind across northwestern Europe changed how they are read. Antiquarians had explained them as cargo lost in accidents or wealth hidden in emergencies; Bradley argued from their patterning, the selection of object types, the frequent deliberate breaking, the repeated use of the same locations over centuries, that they are votive, a religious practice of putting valuable things permanently beyond use by giving them to water. The Thames is one of the richest such deposits in Europe.
The river was also a boundary between peoples, which may be part of the same logic, since deposition often concentrates at edges. When Rome founded Londinium on its north bank the pattern continued in a new idiom: the temple of Mithras excavated at Walbrook, on a stream running into the Thames, had its sculptures of the god and of Serapis and Minerva carefully buried in the temple floor in late antiquity rather than smashed.