INFORMATION
'Salient': a network of fortifications, earthworks and trenches. The Ypres Salient was a famous focus for intense fighting for much of the war.
'paid': here used with heavy irony: there is, in fact, no way of repaying such unaccidental deaths.
'their name liveth for evermore': 'their bodies are buried in peace; but their name liveth for evermore' is a line from Ecclesiasticus (c200AD), a book in the collection of biblical writings known as the Apocrypha. It comes from a well-known passage beginning 'Let us now praise famous men', and also observes, 'some there be which have no memorial; who are perished as though they had never been'.
'immolation': sacrifice
'slime': the poet chooses a word associated with the hellish and disgusting to refer to the mud of the Flanders battlefields

HISTORY
The Menin Gate war memorial at Ypres was built and opened in 1927. It commemorates the British soldiers whose bodies were never found. On its huge panels are carved 54,896 names of men with no known grave who died in this area between 1914 and August 1917. The designer thought there would be plenty of room for all the names, but there was not: a further 34,984 names of missing soldiers (from August 1917 to the end of the war) are carved on panels at Tyne Cot cemetery not far away. The Menin Gate is an integral part of Ypres and the Menin Road, along which people and traffic pass daily, runs through it.

Every night of the year, at 8.00, the road is closed while 'The Last Post', the traditional bugle call marking the end of the day for soldiers in action, is played.

At the opening ceremony in 1927, these words were spoken: 'It was resolved that here at Ypres, where so many of the missing are known to have fallen, there should be erected a memorial worthy of them which should give expression to the nation's gratitude for their sacrifice and their sympathy with those who mourned them. A memorial has been erected which, in its simple grandeur, fulfils this object, and now it can be said of each one in whose honour we are assembled here today: "He is not missing; he is here!" '

The Menin Gate is one of the most-visited monuments on the increasingly well-trodden war memorial tourist trail. Many are drawn by that evening ceremony (which is maintained and carried out by the local Fire Brigade).

IDEAS
Wilfred Owen's poem was a passionate denunciation of war and death in war. This poem by his friend Siegfried Sassoon is a passionate - and angry - denunciation of the way in which the war dead are remembered. He derides the idea that even the grandest memorials in any way recompense 'the poor bloody infantry' for providing cannon fodder - and particularly these men, listed as 'missing, presumed dead', whose 'intolerably nameless' bones are still being turned up by farmers' ploughs in Flanders today.

In four long and terrible years, 'the Dead', once John McCrae's imaginary summoners to vengeance, are now envisaged by Sassoon as posthumously contemptuous of the value which the living place on 'a pile of peace-complacent stone'.

Peace had not in fact been won: the roots of the next war, firmly set in the punishing treaty that ended the last, were sending up shoots as Siegfried Sassoon's poem was being written, and showing signs of flowering when it appeared in the Oxford Book of English Verse in 1936. Sassoon's poem is a reminder that people should never be complacent about peace. The constant work needed to maintain it is as important as the work to achieve it. In that light the constant tending of the world's war cemeteries has become a sad, and painful, metaphor.

Siegfried Sassoon himself became part of the peace movement for a time and was one of the early sponsors of the Peace Pledge Union.