Contemplating an ancient Grecian Urn, the poet Keats describes part of what he sees then asks about the legend the relief scene or painted scene represents. He starts out by addressing whom he interprets to be (or knows to be if he saw the urn and its identification at the British Museum in 1816) a bride before her wedding. He calls her a "still unravished bride" to indicate that she is part of a wedding scene that preceded the consummation of her marriage: the wedding is in progress and still uncompleted.
He styles her the "foster-child of silence and slow time" because she is mute--a piece of speechless art--on an ancient artifact that changes so little across time that it might as well not change at all. He links her to the representation of a forest on the urn by calling her a "Sylvan historian": someone with a connection to a wood that tells a tale of history. Presumably because of her beauty, he says she tells her history "more sweetly" than can his poem, his "rhyme."
Then Keats begins asking questions. We don't know if his questions are mere random speculations or if they indirectly represent what he is looking at or perhaps mentally envisioning. It has been suggested that Keats is actually thinking of a compilation of many urns he has seen in books and at the British Museum, which he visited in 1816. We can tell a few things about the urn--whether imagined, compiled from recollections or seen--that he is describing. First Keats focuses our attention to the "shape" of the bride that is there and the images in the tale or "legend that haunts" about her, images that are over-topped by a leafy garland embellishing the urn, which is "leaf-fringed."
He asks about other shapes on the urn, wondering if they are gods or "mortals." He imagines the scene in the picturesque locations of the Valley of Tempe at the northeast coast of Greece or in Arcady in the southwest peninsula of Greece. He wonders who the "men" and "gods" might be. Might the men be the brides brothers, father and uncles, neighbors? Might the gods be Hymen, the god of weddings, and some local deities? We assume that the scene Keats describes has a collection of shapes that might be "men" or "gods." This supposes a rather large urn and complex scene.
Maidens who are "loth" [archaic spelling for "loath"] are maidens who are strongly reluctant to proceed with something. Perhaps these "loth" maidens are bashful young girls who are engaged in the bridal ceremony and "loth" to be seen so prominently. But what "mad pursuit" could Keats be thinking of, and what "struggle to escape?" Could it be that the bachelors attending the groom's wedding day are out of control and descending on more mature, teen-aged, "loth" maidens who are accompanying the bride and who are struggling to escape the bachelors?
Whoever these shapes are, they are in company with a seemingly large group of pipers and timbrel players. "What wild ecstasy" suggests dancing and frolicking with "loth" maidens" who "struggle to escape" overzealous bachelors. Yet while Keats calls these images to mind, he never returns to them, so we don't know if they are part of the scene or only part of his musings inspired by a more orderly and less complicated scene. We have to expand the scene contemplated from the items specified in the questions or discount the questions as random speculations. Personally, I enjoy the "Grecian Urn" more if I imagine that the "mad pursuit" and "wild ecstasy" of frolicking dancing to pipes and timbrels with "loth" maidens who "struggle to escape" are part of the scene on the urn.