Lore

Lizardmen War

リザードマン侵攻（蜥蜴人の勇者たち）

World & HistoryBattles & Events

Vol. 4, July–August of Year 1 after the transfer (about a month after the Shalltear incident): Nazarick sent Cocytus with an army of low-tier undead against the five lizardman tribes of the great lake in the Great Forest of Tob; after that first battle was lost, Ainz led a large army in person and made them submit, and they became Nazarick's first territory.

After the Shalltear incident, Albedo proposed making stronger undead from demi-human corpses and pointed out that Aura had found lizardman settlements; Ainz ordered Cocytus to "exterminate the lizardmen" with a low-tier undead army.
Nazarick sent a herald to each village to declare war; Zaryusu Shasha, a traveler of the Green Claw tribe, proposed that the tribes unite against the enemy and met Crusch Lulu at the Red Eye tribe.
The five tribes that fought were Green Claw, Small Fang, Razor Tail, Red Eye, and Dragon Tusk; Japanese sources, counting from Vol. 4, total 1,386 lizardman combatants (429 warriors, 26 priests, 45 hunters, 491 males, 389 females, 5 chiefs, and 1 traveler).
The lizardmen fortified the Razor Tail village and won a costly victory, handing Cocytus Nazarick's first defeat; from this he learned to discern his master's true intent and objected to Ainz, after which the policy changed from extermination to rule.
Two days later, Ainz appeared with all of Nazarick's forces and froze the lake with super-tier magic, and Gargantua made its entrance; Cocytus won his duels with the lizardman warriors, and Zaryusu, who was killed in battle, was revived (after refusing once).
After the war the lizardmen came under Cocytus's rule; the five tribes were gathered in the Razor Tail village, Zaryusu's fish farm was expanded under Demiurge's guidance, and a stone statue of Ainz is enshrined in the village's sanctuary.
Other sources state that Nazarick's undead army in the first battle numbered 4,950, and that Cocytus was forbidden to fight in person, was to hold the Elder Liches back until the very end, and had to think for himself (Vol. 4).