The Ancient spellbook is known for spells such as Ice Burst, Ice Blitz & Ice Barrage. This spellbook is used more often than the other spellbooks due to its many offensive, high hitting spells. Players can be found using Ancients in places such as Clan wars white portal and other minigames alike. It is also commonly used for PvP during hybridding fights, in multi-combat player killing and seen seldom used in PvM, the exception being during magic training. (Barraging rock crabs and skeletal monkeys.)
You can switch spellbooks to Ancients by speaking to the Sailor who is located east of Edgeville bank. Praying at the Ancient altar will change your spellbook directly to Ancients (or back to the normal spellbook if Ancients is already activated).