Oath of the fortress.

An Oath of the fortress paladin is one that always has your back and will never let their friends stand in harms way if they have anything to say about it.

Ramparts

When you take this oath at 3rd level, you gain the following.

Summon Ramparts: As a bonus action and once per long rest you can summon three 5ft wide stone walls with 5ft of rough terrain between each of them in front of you in a line running from your left to right. Each stone wall has 70 or 5d20 hp.

The ramparts disappear after 1 hour, if they are all destroyed, or if you chose to have them disappear.

 

Oath Spells

You gain oath spells at the paladin levels listed.

Oath of Devotion Spells

Aura of Protection

Starting at 7th level, you and friendly creatures within 15 feet of you can’t be charmed while you are conscious.

At 18th level, the range of this aura increases to 40 feet.

Grand wall

Beginning at 15th level, all allies excluding yourself within 10ft of you have 1/2 cover against any ranged attacks.

Divine Moat

At 20th level, as an action, you can summon a circular moat with a diameter of 30ft and width of 10ft centered around yourself.

Any creature that starts/ends or otherwise passes through the moat take 1d10+5 radiant damage.

In addition, you also gain advantage on any saving throws against spells cast by fiends or undead from the other side of the moat.

Once you use this feature, you can’t use it again until you finish a long rest.