I think that the answer is coins.
Answer:
a felt, straw, or cloth hat for informal wear having a low telescoped crown, flat top, and brim turned up all around or up in back and down in front.
Explanation:
Corbel dome : arch like construction method to span a space or void in a structure such as a entryway.
Tholos : Beehive like tomb; Burial structure made out of mud bricks and stones.
Rotunda : Round building or dome.
Hope this helps! :)
*cries silently in cuteness*
