The Coelerni were an ancient Celtic tribe of Gallaecia in Hispania (the Iberian Peninsula), part of Calaician or Gallaeci people, living in what was to become the Roman Province of Hispania Citerior, convent of Bracara Augusta (the modern Portuguese city of Braga), in what is now the southern part of the province of Ourense (in Galicia).
Some sources, like Alarcão, also state that the Coelerni lived in the north of modern Portugal, in the province of Trás-os-Montes, in the mountains between the rivers Tua and Sabor - this seems to be incorrect and predates the finding of the Tessera Hospitalis of Castromao. However there was a lusitanian people of the Colarni (inscription of Alcantara) living near the Douro river in Lamego, that could have some link with the galician Coelerni.
The Coelerni are known from few literary sources, such as Pliny and Ptolemy, and because they appear as one of the ten civitates of the convent Bracarensis that are cited in the Inscription of the Peoples of Chaves (the Roman Aquae Flaviae), a column in the Roman bridge in Chaves where those people rend homage to Emperor Vespasian.
Pliny, knew the Iberian Peninsula, as he had worked there as an administrator during the reign of Vespasian. The results of a census he passes on to us informs about the following: «The jurisdiction of Lucus contains 15 peoples both unimportant and bearing outlandish names, excepting the Celtici and the Lemavi, but with a free population amounting to about 166,000. In a similar way the 24 states [civitates] of Braga contain 285,000 persons, of whom besides the Bracari themselves may be mentioned, without wearying the reader, the Biballi, Coelerni, Callaeci, Equaesi, Limici and Querquerni (Naturalis Historia, III, 3, 28).
The main city of the Coelerni was Coeliobriga, now Castromao in Celanova  (Ourense, Galicia, Spain). This Castro was inhabited from the 6th century BC until the beginning of the 4th century CE.
Treaty with Rome
A Treaty of Friendship between the Coelerni and the Romans was made in 132. A Tessera Hospitalis was found stating a pact of hospitality between the tribe of the Coelerni, thus accepting their peaceful integration in Hispania Citerior, and the Roman military commander of the Legion VII Gemina Civitas Limicorum, Gneo Antonius Aquilus Novaugustanus, in exchange for their defence under Emperor Hadrian.
The exact text of the Tessera Hospitalis states: G(neo) IVLIO. SERVIO. AUGURINO. G(eneo) TREBIO. SERGIANO. CO(n)S(ulibus). COELERNI. EX-HISPANIA. CITERIORE. CONVENTUS. BRACARI. CVM. G ( neo). AN TONIO. AQUILO. NOVAUGUSTANO. PRAEF(ecto). COH(ortis). I. CELTIBERORUM. LIBERIS. POSTERISQUE. EIVS. HOS PITIUM. FECERUNT. G(neus). ANTONIVS. AQVILVS. CUM. COELER NIS. LIBERIS. POSTERISQUE. EORUM. HOSPITIUM. FECIT. LEGATUS. EGIT P(ublius). CAMPANIVS. GEMINVS.
Which can be translated as: Being Consuls Gneo Julio Augurino and Gneo Trebio Sergiano, the Coelerni of Hispania Citerior and of the convent Bracari, made a pact of hospitality with Gneo Antonio Aquilino Novaugustano, prefect of the first Cohort of the Celtiberians, with his sons and descendants. Gneo Antonio Aquilo made a pact of hospitality with the Coelerni, their sons and descendants. Acted as legate Publius Campanius Geminus.
- See Jorge de Alarcão, Portugal Romano, Lisboa, 1973 (see page 18 of the 1976 edition) - also published in English as Jorge de Alarcão, Roman Portugal, Warminster, 1988 (in 4 volumes).
- This inscription, made in 79, commemorates the road open by the Legionnaires of the VII Gemina Felix Legion, because that road had been opened with the contributions of ten Civitas, named alphabetically: Aquiflaviensis, Aobrigensis, Bibali, Coelerni, Equaesi, Interamnici, Limici, Naebisoci, Quarquerni and Tamagani.
-  Iunguntur iis Astrum XXII populi divisi in Augustanos et Trasmontanos, Asturica urbe magnifica. in iis sunt Gigurri, Paesici, Lancienses, Zoelae. numerus omnis multitudinis ad CCXL liberorum capitum. Lucensis conventus populorum est sedecim, praeter Celticos et Lemavos ignobilium ac barbarae appellationis, sed liberorum capitum ferme CLXVI. Simili modo Bracarum XXIIII civitates CCLXXXV capitum, ex quibus praeter ipsos Bracaros Bibali, Coelerni, Callaeci, Equasei, Limici, Querquerni citra fastidium nominentur.
- The Tabvla Imperii Romani states (p. 46): «Coeliobriga (Castromao. Celanova) - Importante castro que permite situar Coeliobriga en Castromao gracias al hallazgo de la tessera de hospitalidad entre los Coelerni y el prefecto de la cohors I Celtiberorum, fechada en 132 d.C.».
- Comité Español, Tabvla Imperii Romani. Hoja K-29: Porto. Unión Académica Internacional. Instituto Geográfico Nacional. Madrid, 1991.
- Alonso, Juan L. Garcia, La Península Ibérica en la Geografía de Claudio Ptolomeu, Euskal. Herrika Unibertsitatea, Gasteiz 2003.
- Pliny, Naturalis Historia, III, 3.