What shape is devoid of any definite edges but is enclosed within other shapes? It is not circle, I keep getting it wrong PLEASE HELP

Select one work of art from the gallery that culturally represents the period it was created within. (i choose "the well of moses")why did you select this work of art or architecture? when selecting and writing about your work organize your thoughts by addressing the following questions. keep in mind that the last question should get the most attention in your short essay. when was it made? where was it made? what is the material? who made it? why was it made?