Another... Why was this Built?

Although the craftsmanship of the structure is apparent, I don't know exactly why it was built. I'm going to guess that it's used to feature special plants. From the looks of things though, the landscaping was a work in progress. There was no lawn and very few plants. Inside the square enclosure a lonely shrub could be seen growing. Another thought that came to me was that this could maybe be a small fountain or maybe an unfinished jacuzzi for Roman god worship. It could be a possibility. The house was nice and there are probably plans to remodel the landscaping.