Those umbrella/pinecone things

[Wladimir D]

Upper, middle "the rosette" is similar to the Coliseum. Presumably at the Coliseum was a similar hinged roof. That is,  this rosette depicts the process of collecting rainwater from the roof ( of tent).

The artist is has combined view from the top, and isometric, so in the background is not painted drops, and from the front  flowing "stream".