The full title is "The Imperial War Museum Book of the Somme", where Brown works as a military historian. The book is different from others I have seen on the great battle of the Somme in two ways: first, it traces the history of the Somme theatre throughout WWI, with focus of course on the battle that started that fateful day on July 1, 1916 and continued for months, but Brown also describes the ebb and flow of forces across the area in 1917 and 1918; secondly, it is not intended to be a detailed military history, but rather a contemporary recounting through the voices of the men who participated. Brown achieves this through diaries and letters that Brown compiles from hitherto unknown or unused sources in the Imperial War Museum. The effect is a sense of immediacy in the terror, disgust, joy, fear, satisfaction, patriotism, cynicism, hatred, despair, and jubilation that the participants felt. Fear and cynicism might predominate, but all emotions are evident across the huge number of men who were forced to live through that most awful of crucibles.

On the battle itself, Brown starts off with the opposite views:
"The Somme was just slaughter" versus "The Somme battle raised the morale of the British Army. Although we did not win a decisive victory there was what matters most, a definite and growing sense of superiority over the enemy, man to man....We were quite sure that we had got the Germans beat: next spring we would deliver the knock-out blow". This dichotomy appears throughout the book, but Brown does not shy from showing the poor planning and un-strategic thinking that too often resulted in vast numbers of casualties for no purpose. Only one General, Maxse, comes in for praise for his meticulous planning of assaults. He believed that the danger of word leaking out about an impending attack was greatly outweighed by the danger of sending men over the top without very clear ideas of their purposes and how to go about them. The result was that his troops were much more often successful and with fewer casualties.
I think Brown is right in closing his book the recognition that, "...while recognizing their common humanity, the normality of their dreams and aspirations, it should still be acknowledged that the soldiers of the Somme faced a challenge special to their time and tackled it in their own special way". His final line is a quote from a participant: "There can never be another war like the Great War, nor the comradeship and endurance we knew then. I think perhaps men are not like that now."

And I finally learned (suppose I should have know it before), the source of "Dulce and decorum est, pro patria mori". I once came across a poem by Thomas Moore entitled Pro Patria Mori:

Oh! blest are the lovers and friends, who shall live
The days of the thy glory to see;
But the next dearest blessing that Heaven can give
Is the pride of thus dying for thee.

I wondered if this were the source against which Wilfred Owen countered in his great poem "Dulce and Decorum Est":

...
If you could hear, at every jolt, the blood
Come gargling from the froth-corrupted lungs,
Obscene as cancer, bitter as the cud
Of vile, incurable sores on innocent tongues,--
My friend, you would not tell with such high zest
To children ardent for some desperate glory,
The old Lie: Dulce and decorum est
Pro patria mori.

But the lineage is much longer. The original quote is from Horace (65-8 BC).

Another historical footnote: it was at the Somme, in September 1916 that tanks first appeared in battle.