The banks of the Thames River have hosted human settlements for thousands of years, from Neolithic huts to the soaring skyscrapers of London. Evidence of bygone civilizations has been steadily deposited on the river’s muddy bottom for modern archaeologists to mine.

Now, researchers in London have dated dozens of bones dredged from the river, creating a comprehensive database that has dispelled longstanding theories about why the river came to serve as the final resting place for so many people. The findings were published in the journal Antiquity.

“It’s really fabulous, actually, in lots of different ways,” said Thomas Booth, an expert in ancient genomics at the Francis Crick Institute in London who was not involved in the project. Dr. Booth said it was “by far the most comprehensive effort” to date the human remains found in the Thames.

The river’s mud, which lacks oxygen, is a sealant that helps preserve remains. (If oxygen is present, bones decompose much faster.) And because there is so much activity on the Thames, its mud is constantly yielding historical treasures. In 2018, workers building a new sewage tunnel along the riverbank discovered an intact 500-year-old skeleton with leather boots still on its feet.

For the new study, researchers dated bones by measuring the amount of a carbon isotope in each one. This method, known as radiocarbon dating, had previously been used to determine the age of 19 samples. This time, the researchers tested 28 river samples — all from skulls — that had never been dated before. They also tested two skulls from a decades-old investigation to see if the results still held up (they did).

The researchers also included some samples that had been found by “mudlarks,” amateur archaeologists who are deputized by London officials to scour the Thames. (It’s a popular hobby; some 10,000 people are on the mudlark waiting list).

In all, the researchers compiled 61 dated samples in their database. About 200 other samples from the river have not yet been dated, they said.

“It’s the largest assemblage of its nature in Britain,” said Nichola Arthur, an author of the study and an archaeologist at the Natural History Museum in London, which contributed the 28 new samples.

The Romans settled London (then known as Londinium) shortly after conquering Britain in 43 A.D. Remarkably, traces of the Roman settlement still remain, such as a basilica just discovered under the city’s financial district.

But humans lived along the river long before that.

“There were people settled here nearly 4,000 years ago,” said Heather Bonney, another archaeologist at the Natural History Museum and author on the new paper.

Half of the new samples came from either the Bronze or Iron Age, which stretched from 2300 B.C. to the arrival of the Romans, with a notable cluster appearing amid the transition between the two periods. This led them to conclude that the bodies had been placed in the river intentionally, contrary to previous theories arguing that they had been moved by powerful tides.

The study also sheds light on archaeology’s “missing dead” conundrum, referring to a dearth of evidence about the funerary practices of many ancient societies. If water burials were as prevalent as the Thames findings suggest, the rivers of Europe could be doing double-duty as prehistoric graveyards.

“Part of the reason why the dead are invisible in this period is that a lot of them are being deposited in rivers or other watery places,” Dr. Booth said.

As far as other watery places, bogs have been an especially rich source for archaeologists, since their acidic waters allow for an astonishing, mummy-like level of preservation. Britain’s most famous bog body is the Lindow Man, who was discovered in 1984 and is thought to have been the victim of a violent death around the time of the Romans’ arrival. None of the Thames bones have achieved his level of fame.