This Aroma Burner with the lid on top resembles the shape of a Chedi or stupa. It is the most important and sacred structure of a Thai temple which used to contain relics of the Buddha. Later on, they were also used to enshrine the remains of Kings or a very important monk.
Chedis are found in various shapes and variations. The most used chedi style in Thailand is the bell shaped form, similar to this Aroma Burner.