Detailed Instructions: In this task, you're given a passage, further information available on a particular linked term from the statement, and an answer term. Your job is to generate a question that can use the information provided to obtain the given answer. You should use the information on both passage and link information to create the question. Note that the answer to the question should be exactly the given answer, and if the answer is none, the answer to the question shouldn't be obtainable from the passage or linked information.
Q: Passage: After his term as consul, Didius was assigned to govern the province of Hispania Citerior, where he served from 97 BC to 93 BC. Nearly his entire proconsular term in Spain was spent at war with the Celtiberi. In the four years Didius governed Spain he achieved multiple victories and is said to have slain 20,000 Arevaci, quelled the rebellious city of Termes (today Tiermes in the province of Soria), and besieged Colenda for nine months, after which time the city fell and the women and children were sold into slavery. Didius earned another triumph after slaughtering a colony of "robbers" -- in actuality, poor people who had banded together to subsist through banditry after losing their property. Didius lured them in with promises of land to live on, and when the families assembled within the Roman castra in good faith, he had them all killed. The historian Appian indicates that Didius's exceptional cruelty and treachery caused an even greater uprising which his experienced successor, C. Valerius Flaccus, had to put down.
Link Information: Appian began writing his history around the middle of the second century AD. Only sections from half of the original 24 books survive today. Answer: 24
A:
How many books were written by the historian that remarked on Didius's treachery?