Conflagration

Choose a square section of terrain you can see within range, 10ft on a side. Within this 10ft square, potent flames erupt from from the ground, scorching earth and stone and igniting any flammable materials in their vicinity. The flames burn without fuel for the duration, and as long as you maintain concentration, you may expand the area of of the inferno by 50sqft (two 5x5ft tiles) as a bonus action at the end of each of your turns. The tiles must be adjacent to part of the area that is already burning, but may be placed separately. A creature who enters the area affected by Conflagration for the first time, or ends their turn in the area, takes 8d6 fire damage.

Breaking concentration. If the caster stops concentrating on the spell before the end of its full duration, the flames persist for a number of rounds equal to the number of rounds that concentration was maintained for, and then disappear. For example, if a caster concentrated on the spell for three rounds, including the round when they first cast the spell, and then lost concentration, the flames would remain active until the end of the casters' turn on the 6th round from the time of casting. If concentration is maintained for the whole duration of the spell, the flames persist for an additional 4 minutes, for a total of 5 minutes. In any case, when the flames expire, they disappear as if the fuel that had been feeding them was abruptly removed. Any flammable materials that where ignited by conflagration continue to burn.

Artificer: Greek Fire. An artificer with the alchemist subclass can take this spell, and when casting it, they throw a vial of Greek Fire which in all other ways behaves the same as the spell normal would.