Short answers, pulled from the story.
The Celtiberians were a group of Celts and Celticised peoples living in the central-northeastern Iberian Peninsula during the final centuries BC. Classical authors such as Strabo described them explicitly as Celts, and they spoke the Celtiberian language, a Hispano-Celtic tongue.
The Celtiberians spoke Celtiberian, a Hispano-Celtic language related to other Celtic languages once spoken in pre-Roman and early Roman Iberia. They wrote it by adapting the Iberian alphabet into what scholars call the Celtiberian script.
Rome began conquering Celtiberia in 195 BC and had absorbed the entire region into the province of Hispania Citerior by 72 BC. Celtiberian tribes rose up repeatedly in the meantime, in uprisings dated 195-193 BC, 181-179 BC, 153-151 BC and 143-133 BC.
In 134 BC, the consul Scipio Aemilianus besieged Numantia with about 60,000 Roman troops spread across seven camps. After eight months the starving Numantines were reduced to cannibalism, and many killed themselves rather than surrender before the town was razed.
Celtiberian two-edged swords were prized for their strong, double-edged points, and Rome adopted their construction after the Hannibalian War. According to Varro, the Latin word lancea, meaning a thrown spear, was also a Hispanic term.
A genetic study published in Science in March 2019 examined three Celtiberians buried at La Hoya, in Alava, between 400-195 BC. It found they carried notably high levels of north-central European ancestry, with one man carrying the paternal haplogroup I2a1a1a.