The Epidii (Greek: Επίδιοι) were a people of ancient Britain, known from a mention of them by the geographer Ptolemy c. 150. Epidion has been identified as the island of Islay in modern Argyll.^[1] Ptolemy does not list a town for the Epidii, but the Ravenna Cosmography (RC 108.4) mentions Rauatonium, which is assumed to be Southend.^[2]

The name Epidii includes the P-Celtic root epos, meaning "horse" (c.f. Welsh ebol, "a foal").^[3] The Q-Celtic equivalent would be *ekwos, which became Old Gaelic ech. It is suggested that they were named after a horse god, whose name could be reconstructed as *Epidios.^[4] The Q-Celtic equivalent would be *Ekwidios, which may be the origin of the Old Gaelic name Eochaid.^[4]

The Dagda, a Gaelic god, is often referred to as Eochaid Ollathair.^[5]

Although their name is almost certainly is Brittonic/P-Celtic, Dr Ewan Campbell suggest they were Goidelic/Q-Celtic speakers. He says "Ptolemy's source for his Scottish names was probably from the Scottish Central Lowlands, and may have transmitted the Brittonic form of a Goidelic tribal name, or even the external name given to the tribe by Brittonic speakers".^[6] Their territory later became the heartland of the Goidelic kingdom of Dál Riata. Alex Woolf suggests that the Epidii became the Dál Riata, but argues that they were Brittonic-speaking in Ptolemy's time.^[4] He also suggests that the Hebrides, called the Ebudae by Ptolemy, were named after the Epidii.^[4]

• Britons (historic)
• Picts
• Scottish people
• Dál Riata