See, I think we need to take a fresh look at this image.
Here is my proposal, I don't have the time to write it out with more reasoning at the moment so I'm just going to witter on:
I think we're looking at a fortified medieval town, fed by two aqueducts (1 and 2) (the "walls" sweeping either side). You can see that the "walls" are multi-layered, in the fashion of aqueducts. I doubt that the blue line on top indicates water, as it's used elsewhere just to provide perspective. The walls of the town have windows (indicated by || ). They must be high, as they are two stories above the door.
The art reconstruction shows the aqueduct arches of New Anio, crossing the loop of the Juliev aqueduct, directly over the Via Latina road leading from Rome. From "Roman Architecture and Urbanism" (C.U.P.)
I don't think it's a castle, as the two watchtowers that surround the town are
outside of the walls and are clearly not part of the fortifications. I don't think they are fortifications; they are part of the aqueducts.
The town has a single, very high (count the number of windows indicating stories above the wall) tower with a conical roof (3), possibly with battlements, although a number of these conical roof towers had overhangs and we could be seeing this. The conical roof is a very strong clue, as most of the medieval Italian towers had flat roofs. There must have been a specific reason for drawing a conical roof, and it could be as simple as the one outside the illustrators home had one, so that was his inspiration! It is drawn in a very different way to the watchtower on the wall (6), which has a very strong pyramidal roof with walk around.
The town has a fortified wall (7) spanning out from its left side, which is guarded by two small castles (4 and 5) and in the middle a watchtower (6). The wall (7) sweeps around the "star of fields".
Is it a real place? I would suggest it isn't. It's an allegory, a town that is protecting whatever the "field of stars" is supposed to represent and through which the traveller must pass to reach it (note the prominent door). That said, it is using real-world elements the illustrator understood, probably from seeing them in daily life (Ghillibini merlons, the aqueducts, the tower). Viewed in this fashion, it has a strong medieval Italian flavour.
But it would be interesting to find a medieval walled town with Ghillibini merlons, a coned tower and two aqueducts.
Of course, if we accept that this has a strong Italian influence, this contradicts other imagery elements such as the Sagittarian crossbowman,
which appears to come from Germany. This could be explained by postulating two illustrators; but I'm rambling now so I'll stop.