Just finished reading Truchman's guns of August (fantastic read BTW), which stops at the French counterattack on the Marne. I've also read Alistair Horne's excellent account of Verdun in 1916, and several other books dealing with various aspects of WWI. But now I am looking for recommendations on a book that is specifically focused on the first battle of the Marne. Anyone got a good one? What are the timeless classics on this battle?