Four entries with the name Red City.
Red City
Rouge Citié
The castle ruled by Sir Partinal, an enemy of Perceval’s family. Perceval killed him there.
Source
Third Continuation of Chrétien’s Perceval | Manessier, c. 1230
Red City
Cite Vermeille
Esclamor of the Red City is its ruler.
Source
Vulgate Lancelot | 1215-1230
Red City
Vermiglia
A city on the Delectable Isle, off the east coast of Britain, ruled by King Armant.
When two of Armant’s protégés killed Armant and seized the city, Sir Palamedes (Palomides) avenged the deed, became lord of the Red City, and gave the city to Marin, Armant’s brother.
Phyllis Ann Karr thinks the Red City might be Kilnsea, if King Hermance’s Delectable Isle is the Spurn Head peninsula in East Riding.
Sources
Prose Tristan | 1230-1240
La Tavola Ritonda | 1325–1350
Le Morte Darthur | Sir Thomas Malory, 1469-1470
Red City
A King of the Red City was defeated by Erec at the Tenebroc tournament in Chrétien’s Erec.
He may have inspired Hartmann’s Roiderodes.
Source
Erec | Chrétien de Troyes, late 12th century