[split] Taccola spillover thread

[Koen G]

One nuance is that a hypothetical copy for Sigismund would have been given to the Emperor upon his visit to Siena, after which he travelled back north. These are my current thoughts on our three options:

1. Pre-1433 common source. Note that this cannot just be any book on public water infrastructure. That is to say, there are a lot of details both in contents and style that make the Taccola bridge parallel so strong. The vertical ravine, the vertical lines along the edges, the technique used to draw the undulating stream... All of this comes on top of the layout parallels. If an older common source exists, we have not seen it yet.
   
2. Copied from Taccola's work in Siena. If he had earlier sketches (which he did), we can push this a bit before 1433. In fact, it is said that work on his four books started as early as 1419. But I assume a more general accessibility of the work in university circles can be assumed from 1433 onward.
   
3. Copied from Emperor's copy. If a copy was given to the emperor, this happened in 1432-1433. I guess the timer starts ticking at that point, since anyone in the emperor's surroundings could theoretically have seen the MS or copied from it.
   

All of those are speculative, we only know for sure that:
* The work was completed in Siena in 1433 and very likely kept there.
* The work was shown to the emperor at the same time.