The archetypal Stalwart mixes the same fundamentals of a unmounted Cavalier with an oppressive pavise, targe or hoplon to upset martial enemy formation, provide pressure and protection. Traditional wisdom dictates that a shield wall is weakest when its fighters are separated; not so for the lone bastion, the Stalwart. Careful conditioning has helped these fighters to manage the burden of heavy shields and unwieldy weapons, using stance changes to keep up with an evolving battlefield. 

Level 3: Shield Stance

At level 3 you gain the ability to craft and repair a specialized tall shield and you can alter a magical shield into a tall shield with 5 days of effort. When wielding this shield and not mounted, prone, restrained or incapacitated, you lose 15 ft. of your movement speed and gain the following benefits:

• You can ignore the "two-handed" property of reach weapons that do piercing damage
• You gain +2 to Dexterity saving throws
• You gain advantage on saving throws against being knocked prone
• As a reaction, when struck by a melee attack you can immediately make an unarmed strike with your tall shield and add your proficiency bonus to the damage

Level 3: Unwavering Mark

Starting at 3rd level, you can menace your foes, foiling their attacks and punishing them for harming others. When you hit a creature with a melee weapon attack, you can mark the creature until the end of your next turn. This effect ends early if you are incapacitated or you die, or if someone else marks the creature with this feature.

While it is within 5 feet of you, a creature marked by you has disadvantage on any attack roll that doesn’t target you.

If a creature marked by you deals damage to anyone other than you, you can make a special melee weapon attack against the marked creature as a bonus action on your next turn. You have advantage on the attack roll, and if it hits, the attack’s weapon deals extra damage to the target of the weapon's damage type equal to half your fighter level rounded down.

You can make this special attack on marked creatures a number of times equal to your Strength modifier (minimum of once), and you regain all expended uses of it when you finish a short rest.

Level 7: Sturdier than Thou

At 7th level, you learn to use the weight of your shield to its full potential. The following effects are added to your Shield Stance:

• You have advantage on Strength saving throws
• Whenever you make an Unarmed Strike and choose to damage, it acts as a shove as well. 

Level 10: Heroic Warrior

The thrill of battle drives you toward victory. During combat, you can give yourself Heroic Inspiration whenever you start your turn without it.

Level 15: Superior Critical

Your attack rolls with weapons and Unarmed Strikes can now score a Critical Hit on a roll of 18–20 on the d20.

Level 18: Survivor

You attain the pinnacle of resilience in battle, giving you these benefits.

Defy Death. You have Advantage on Death Saving Throws. Moreover, when you roll 18–20 on a Death Saving Throw, you gain the benefit of rolling a 20 on it.

Heroic Rally. At the start of each of your turns, you regain Hit Points equal to 5 plus your Constitution modifier if you are Bloodied and have at least 1 Hit Point.