Note the tent-pole finials, each in the shape of a sphere on a short stem. All the tents are decorated with vertical, dark-colored stripes, with rows of colored triangles along the edges of the door and geometric or heraldic patterns at the shoulder. Notice also that the main guy-lines come from three-way "crow's-feet" attached through dark grommets at the top of the decorative shoulder-strip. All the tents are apparently circular, and one has a visible center-pole. For the furniture buffs, the Roman Emperor Julian is sitting in a (perhaps folding) throne in the form of a curved X-chair decorated with gold lions, with his feet resting on a carved wooden box.
Here's a detail of the foreground group,
including most of the front tent.
Thanks to Stephen Wyley, who found this picture at the Web Gallery of Art; thanks also to Emil Kren and Daniel Marx of the Web Gallery of Art, whose scan (above) I copied from their Web page on Simone Martini.