This is the classic text on medieval, and later, crossbows. Published in 1903, it has recently been reprinted.
Although mainly on crossbows, the book also has good coverage on many
The author is a Czech and, despite the title, it's probably better described as "Castles of Europe and Britain", especially those of Eastern Europe. Being familiar with medieval British castles, but largely unaware of the later Baroque castles of Europe, I found it fascinating.
Large format and well illustrated, this book gives a fine overview of castle building and changes in their defenses over history.