Duro- was a common place-name element in early Britain.  See the following names individually for their observed spellings and for evidence about their locations, as distinct from the over-simplified forms and locations shown here:
Durobrisin            Scole
Durobrivae           Chesterton
Durobrivae           Rochester
Durocobrivis        Dunstable
Durocornovium    Cirencester
Durolavi               Halesworth
Durolevum           Ospringe
Duroliponte          Cambridge
Durolitum             Chigwell
Duronovaria         Dorchester
Δουροτριγες         Dorset people
Duroviguto           Baylham Farm
Durovernum         Canterbury
Duriarno              Nanstallon
Durcinate             Stratford St Mary
Bdora                   Sandy Wath
Lactodoro             Towcester
Purocoronavis      Bude

It also occurred in relatively Germanic regions on the Continent.  Examples include:
in Belgica at Durocatalaunum (Châlons-en-Champagne), Durocortorum (Reims), Duroicoregum (Domqueur), Duronum (Etroeungt), and Durocassium (Dreux);
beside the Danube at Durostorum (Silistra) and Βοιόδουρον (Passau); and in the Alps at Durotincum (Villar d'Arâne).

Endlicher's Glossary of “Gaulish” translated Doro as Latin Osteo ‘entrance’, possibly based on a document from the AD 500s that glossed isarnodori (referring to modern Izernore near Geneva) with Latin ferrei ostii ‘iron gates’.

Duro- came from PIE *dhwer- ‘door’, which is cognate with forum, also originally something one passes through.  Words meaning ‘through’ (German durch, Dutch door, etc) are attributed to a different PIE root, but that is debatable.  The bad old idea that duro- meant ‘fort’, related to Latin duro ‘to make hard’, is still sometimes repeated, but now it is rationalized on the basis that forts had gates and/or markets!

The common geographical feature of all duro- places in Britain is a crossing, generally over water.  Durocobrivis (Dunstable) is interesting, because the Roman road there runs on dry land between (hence presumably the -co- part) two edges (brims or brinks, the brivis part).  *Durotincum was on a Roman road that is now the very scenic D1091 through mountains in south-east France, with just lots of small mountain streams to cross.  The name durotincio on an inscription has led to a suggestion that that there was another *Durotincum near Limoges.  Celtic scholars cannot explain the element tinc-, perhaps through unwillingness to consider the very Germanic ting ‘popular assembly’.

Now here is a list of ancient place names ending in -durum (or similar).  Rivet (1980:14) listed altogether 39 such names, but some of them are very doubtful, and only some are included here.
*Albiodurum           Augers-en-Brie                   northern France
Augustodurum        Bayeux                                Normandy
Autessiodurum        Auxerre                               (in Celtica)
Batavodurum          Nijmegen                             Netherlands
Boiodurum              Passau-Innstadt                   Inn x Danube
Breviodurum           Brionne                                Normandy
Brivodurum             Briare                                  central France
Divodurum              Metz                                    NE France + same name at Jouarre etc?
Epamanduodurum   Mandeure                            river Doubs near F/CH border
Ernodurum              Saint-Ambroix-sur-Arnon   Central France
Ibliodurum              Ville-sur-Yron?                    Belgica
Iciodorum                Yzeure                                 central France
Ictodurus                  La Batie Neuve                   Alps
Ilduro                       near Mataro                         Spain
*Isarnodurum          Izernore                               eastern France
Lactodurum             Towcester                            Watling Street x river Tove
Nemetodurum          Nanterre                               near Paris
Octodurus                Martigny                              Switzerland     lookout (Oc-) on the Rhone
Oktodouron              ?=Ocelodurum ?=Zamora   Spain
Salodurum               Solothurn                             Switzerland, on the Aare
Sorviodurum            Straubing                             Bavaria     vulnerable to floods
*Turnodurum           Tonnerre                              France
Teudorum                 Tüddern                               Dutch/German border     compare touta/Deutsch
*Venaxamodurum    Neuburg an der Donau        Bavaria
Vetatodurum             Vellerot-les-Belvoir            Burgundy
Vitudurum                 near Winterthur                  Switzerland

An outlier beside the Euphrates at Dura-Europos probably embodies a Semitic root dur ‘to dwell, to move in a circle, to heap up’.  Sallust mentioned people called Mutudurei during Pompey's campaign in Spain.

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