Nautilus is a robust tank champion in League of Legends, known for his crowd control and ability to absorb damage for his team. The build you’ve outlined is focused on maximizing Nautilus' tankiness, providing immense protection for your team, and enhancing his utility as a frontline initiator and engager.

Core Items:
Sunfire Aegis – This item grants Nautilus health, armor, and a passive burn effect that damages enemies around him. It greatly enhances his durability while also dealing damage over time in fights.
Locket of the Iron Solari – This item provides Nautilus with bonus health and resistances, as well as an active shield for nearby allies. It helps mitigate incoming damage and protect your team during engagements.
Knight’s Vow – Ideal for protecting a priority ally, this item links you to them, redirecting a portion of the damage they take to you. It also provides health, armor, and a helpful damage reduction aura for your teammate.
Thornmail – Thornmail offers armor and a passive that reflects damage to enemies who hit you, which is especially effective against champions who rely on auto-attacks or healing. It’s particularly useful against AD (Attack Damage) and healing-based champions.
Plated Steelcaps – This boot choice provides armor and reduces incoming damage from basic attacks, especially against AD-heavy teams, while also enhancing Nautilus’ tankiness in the early to mid game.
Steelheart – This item grants Nautilus health, bonus resistances, and a passive that increases his health for each enemy champion nearby. It scales well during team fights, making Nautilus more tanky as he stays in combat.
Situational Items:
Frozen Heart – A powerful option for slowing down enemies’ attack speed while also providing additional armor. It’s useful when facing auto-attack reliant champions or teams with high attack speed.
Warmog’s Armor – This item provides an immense amount of health and health regeneration, making Nautilus even more difficult to take down in prolonged team fights. It’s especially useful for sustained engagements.
Zeke’s Convergence – Zeke’s provides bonus health, resistances, and an active that enhances the damage output of an ally while also empowering their basic attacks. This is great for bolstering the damage output of a carry.
Abyssal Mask – This item grants magic resist, health, and a passive that reduces the magic resist of nearby enemies. It’s useful against teams with heavy AP (Ability Power) damage dealers.
Randuin’s Omen – Randuin’s offers health, armor, and a passive that reduces critical hit damage and slows down enemies around you. It’s a great pick against enemy carries who rely on critical strikes and auto-attacks.
Runes:
Aftershock (Primary Keystone) – After landing a crowd control ability, Nautilus gains bonus resistances and deals damage around him, enhancing his tankiness and helping him deal additional damage during fights.
Secondary runes like Font of Life and Conditioning are ideal for scaling well into the mid and late game, helping Nautilus provide healing to his team and making him even tankier as the game progresses.
Playstyle:
This build focuses on making Nautilus an unkillable frontline tank who not only absorbs massive amounts of damage but also supports his team with crowd control and protection. The synergy between Knight’s Vow, Locket of the Iron Solari, and Steelheart makes Nautilus a solid protector for key teammates, while Thornmail and Frozen Heart help deal with attack damage threats. Additionally, Zeke’s Convergence and Abyssal Mask offer utility to empower carries or weaken enemy magic resist, ensuring that your team has both defense and offense.

This tank build allows Nautilus to be a true frontline juggernaut, soaking up damage, enabling engages, and providing unparalleled protection for his team.