Large Scale C++ Software Design by John Lakos.

This is the most important book which any C++ programmer could read, and most people have never even heard of it.

It covers in pain-staking detail the physical dependencies which flow from the C++ language design, and how to write truly modular C++ code. Most people have never read the book, and repeatedly fall into the same language traps, leading to the truly abysmal compile-link cycle of most C++ software.