"Theory and Practice of Fortifications" by Captain Cristobal de Rojas, 16th Century

Captain Cristobal de Rojas (1555-1614) was born in Toledo, Spain, and is considered one of the most significant militar architect and engineer, due to the large amount of treatises he wrote about this matter during 16th Century. He specialized on fortifications for defense against pirates and corsairs, after the looting of Santander by "Sir" Francis Drake. His talent was soon detected by his commander, and initiated a long trip to inspect fortifications of Gibraltar, Ceuta, Tarifa, Lisboa, Cadiz... was after the inspection of Cadiz fortification when he made several recommendations that were not considered by the Spanish Royal Navy, even when he insisted passionately to militar authorities and the King. Only three years later this important city was almost destroyed by British Admiral Howard. After that, his talent was recognized by the King Felipe III, and started a military career in which he travelled around the world planning deffenses and fortifications for the Spanish imperium.

The most important treatise of Captain Cristobal De Rojas is “Theory and Practice of Fortifications”, printed in 1598 in Madrid, with Royal Privileges.

Quattro Libri dell'Architettura (The Four Books of Architecture, 16th Century)

This is probably the most ambitious treatise on Architecture ever published. Was composed by Andrea Palladio (1508-1580) in the Republic of Venetia and served as a reference for Architects all over Europe and America even nowadays. Palladio influence became fashionable all over Europe, for example in parts of the famous Loire Valley of France, Britain, Italy, Spain, and later to the new America, especially for Southern States cotton farms. In his Italian Journey, Johann von Goethe describes Palladio as a genius, commending his unfinished Convent of S. Maria della Carita as the most perfect existing work of architecture. Another Palladio admirer was the architect Richard Boyle also known as Lord Burlington, who, with William Kent, designed Cheswick House. The US Capitol building is an example of slightly evolved version of Palladio's works –a replica of this building exists also in Havana, Cuba-. Thomas Jefferson loved this style of architecture and considered also Andrea Palladio as a genius.

Andrea Palladio complete bio is available on the Wikipedia (very detailed), link is here. As a briefing, two remarkable facts: 1) He was strongly influenced by Roman and Greek Architecture (primarily by Vitruvius) and 2) He was incredibly prolific: see the Wikipedia reference list for all Villas, Palaces (Palazzos), Domes, Churches, Theaters and even bridges (pontes)… 

First Book has basics regarding choice of materials, rules of proportion, etc. Second Book has a compilation of projects with a specific description, third Book has specific guidelines for public buildings and infrastructures and fourth Book has a collection of ancient Roman temples, which has been used as a reconstruction of the archaeological remains and ruins of the immortal Rome.