Arcane Caltrops

You conjure arcane caltrops to fill a 5-foot cube in a space that you can see within range.

Until the spell ends, any creature that enters the area or moves through the area must succeed on a Dexterity saving throw or stop moving and take 1 piercing damage. Taking this damage reduces the creature's walking speed by 10 feet until the creature regains at least 1 hit point. A creature moving through the area at half speed doesn't need to make the save, and takes no damage.

For every character level above 1st level, the caster can fill an additional 5-foot cube which you can arrange as you wish. Each cube must have at least one face adjacent to the face of another cube. A creature triggers an additional save for each additional 5-foot cube it moves through.  Taking this additional damage reduces the creature's walking speed by an additional 10 feet until the creature regains at least 1 hit point.  If a creature's speed is reduced to moving at half speed or less the creature no longer triggers the dexterity saving throws and takes no additional damage from this spell.