The big stupa here is impressive, and very old. You can never be too sure how old something is in Thailand, because time is not important here. The literature says that this temple complex was "possibly" built during the Ayuthya Period, based on the architecture. It was seven or eight hundred years ago anyway.
These are Indian style, bell-shaped stupas.
The big one is surrounded by an ocean of smaller ones. They're individualized with dedications, some have pictures of the dearly departed one. So I think they're memorials purchased by families, or the loved one himself, in life.