Barkskin

Level: 2

Casting Time: 1 action

Range: Touch

Duration: Concentration, up to 1 hour

You touch a willing creature. Until the spell ends, the target's skin has a rough, bark-like appearance, and the target's AC can't be less than 16, regardless of what kind of armor it is wearing.

Source: PHB, page 217. Available in the SRD.