So where was Ramelli?

Assuming that Ramelli stayed with the Marquis of Marignano until after the siege of Siena, we still have a number of years to account for. Here are some options:

1. He may have worked with Henry I, Duke of Guise, on the restoration of the fortifications of Metz. He may have stayed in Metz during the construction of the citadel (1552-1562). He may have stayed on with Henry I through the Battle of Saint-Denis in 1567, Jarnac, and Moncontour in 1569, where he may have met Henry II, then the Duke of Anjou. The tensions between Henri II and Guise didn't really start until after the Edict of Beaulieu and the formation of the Catholic league.
2. He may have stayed in Italy, perhaps working with Pius IV, the brother of the the Marquis de Marignano, on plans for fortifying Bologna (a project first envisioned by Antanio da Sangallo the Younger in the 1520s). The pope charged his cousin, Gabrio Serbelloni, to review the fortifications throughout the Papal State. In December 1561, Serbelloni ordered a repairs of the medieval walls, the construction of two bastions, and the installation of earthworks. The work was entrusted to a papal captain, Giovan Giorgio Lampugnani and Scipione Dattari, the chief municipal engineer, was named architect. The Bolognese resisted. In 1563 or 1564 the military architect Francesco Laparelli noted that the earth works had been completed but the city remained very weak. The Bolognese called in their own military expert: Plinio Tomacelli, a native of Bologna who had advised both Gian Andrea Doria and Philip II of Spain. He wrote a discourse that refuted the need for fortifications noting that Bologna had walls to defend against skirmishers and would have sufficient time and resources to prepare additional defenses in the even of a full scale attack. His discourse stresses the importance of loyal citizenry and demonstrates Machiavellian leanings. With the death of Piux in December of 1565, construction stopped. (see Tuttle, Richard J. (1982). Against fortifications: The defense of Renaissance Bologna. The Journal of the Society of Architectural Historians. 41.2: 189-201)
3. Perhaps he journeyed to the "cockpit" of fortifications: the Spanish Netherlands. His book certainly pays a great deal of attention to pumps for dewatering foundations and marshes. I'm just not sure how he would have gotten there. Perhaps with Phillip II after the abdication of Charles V.
4. Turin is another possibility. Francesco Pacciotto began working on the citadel in 1564 on the orders of Emanuele Filiberto of Savoy. Pacciotto also constructed the citadel of Antwerp in 1567. Perhaps he is the lowland connection. This approach may also explain how Ramelli transitioned from the employ of the Medicis and the Roman Empire to that of the French king. There is other evidence for his presence in Turin such as the presence of an unpublished manuscript copy of another work in the hand of Ramelli.
   

I need to bone up on my knowledge of Siena, Bologna, and the Dutch Revolution. But we'll get there.