The Menin Gate is one of four memorials to the missing in Belgian Flanders which cover the area known as the Ypres Salient. Broadly speaking, the Salient stretched from Langemarck in the north to the northern edge in Ploegsteert Wood in the south, but it varied in area and shape throughout the war.
The site of the Menin Gate was chosen because of the hundreds of thousands of men who passed through it on their way to the battlefields. It commemorates casualties from the forces of Australia, Canada, India, South Africa and United Kingdom who died in the Salient; in the case of United Kingdom casualties, primarily those prior 16 August 1917. United Kingdom and New Zealand servicemen who died after that date are named on the memorial at Tyne Cot.
The memorial, designed by Sir Reginald Blomfield with sculpture by Sir William Reid-Dick, was unveiled by Lord Plumer on 24 July 1927 and bears the names of more than 54,000 officers and men whose graves are not known.
More information about this memorial can be found on the Commonwealth War Graves Commission website.