The answer lies in the fact that about 250,000 years
ago the whole of Cambridge city as we know it now was covered by the floor
of a river valley. It was very different to the river Cam that we see
today; it consisted of lots of channels separated by small gravelly islands
and banks that shifted all the time.
A braided river in New Zealand
Certain conditions can make this type of braided
river 'jump' to a different course - particularly after violent melting
snow floods, which is what would have happened to the river Cam in Ice
Originally, the braided river flowed north along Hills
Road, Regent Street, straight through the city centre, and past Castle
Hill along Huntingdon Road - pretty much perpendicular to the present
river! The gravelly river deposits found on top of Castle Hill
actually used to form the bottom of the braided river valley...
What was the bottom of a valley is now the top of a hill!
This startling landscape change is called 'inversion
of relief' or 'inversion of topography'. It appears that the river gravels
formed an armoured layer that slowed down erosion compared to the rapid
erosion of the relatively soft bedrock (chalk and clay) of the surrounding
Further along Huntingdon Road near the Beefeater pub
and restaurant, is the Traveller's Rest Pit. This site produced worked
flint tools, along with gravels from an earlier course of the proto-Cam
which flowed here some 300 to 400,000 years ago. You can see artefacts
from the pit in the Sedgwick
Museum of Earth Sciences and the Museum
of Archaeology and Anthropology.
This high ridge of gravel, stretching from Huntingdon
Road, past the Beefeater, through Girton College and Girton village is
one of the most ancient alignments of the ancient river Cam and can very
reasonably be regarded as the 'great-grandfather' of the present Cam!
Looking up Castle Hill
A city is born
As the Romans first arrived in Cambridge in AD 70, they were travelling
north from Colchester, trying to avoid the wet and marshy Fens to the
east. They arrived in Wandlebury and looked down on a very, very muddy
They would have seen Castle Hill in the distance, and
rather than go round the muddy swamp below, they preferred to go in a
straight line right across. Imagine them going past Addenbrooke's Hospital,
along Regent Street, crossing the river at the Quayside, then up past
Shire Hall and off towards Godmanchester!
So Cambridge began on top of Castle Hill as a Roman garrison
guarding a river crossing on the road to the north. Having such a high
view point was a strategic advantage for early settlers which is why the
Norman's made the most of this natural hill by building a motte and bailey
castle upon it. In fact you can still see the motte - the castle mound
People began to live on the hill including the Saxons
who later settled down on the river valley on the gravel and mud. Cambridge
grew as a Scandinavian trading centre and flourished as an inland port.
If you look at the city coat of arms you'll see ships, sea horses and
bridges which are a reminder of the importance of the river. The town
was founded as a river crossing and it flourished because the river was
the equivalent of the M11 of its day!
A 360° view of the city!
Castle Mound is a rare example of chalk grassland close to a city centre.
It's a great place to look out and see how green Cambridge is. It's also
a great place to look out for birds including birds of prey, swifts, sparrow
hawks and house martins. Grasshoppers and butterflies thrive on the sunny
slopes and there's also an enormous population of small black and white
snails. The trees that you can see from the mound include fruit trees,
birch trees and sycamores - and the interesting-looking tree at the bottom
is called a Cedar of Lebanon.
Walk down Castle Hill until you reach the cross-roads
at the junction with Chesterton Lane. On the opposite side of the road
you'll see a big tall monument.
The Saxon monument
About four years ago this part of the road had to be
dug up. This site where the monument stands would have been just off the
path of the Roman road, so rather than digging through 800 years of road,
they were going through 1500 years worth of human habitation! As they
went down they went through medieval houses and the archaeologists found
gold treasure... perhaps some medieval merchant had hidden his stash and
forgotten about it! At the bottom they found bones of a Saxon graveyard
and it's a reminder that for centuries, Castle Hill was Cambridge. It
was where people settled above the valley. Castle Hill began as the administrative
centre for this area and it still is - with Shire Hall there today.
Turn left at the junction and keep walking along Chesterton
Lane until you reach the pedestrian crossing where you can cross over
the bridge to get to Jesus Green.