Tomb of the Unknown Soldier
In many wars, huge numbers of soldiers have died without their remains being identified. In modern times the practice developed for nations to have a symbolic Tomb of the Unknown Soldier that represented the war grave of those unidentified soldiers. They usually contain the remains of a dead soldier who is unidentified (or "known but to God" as the stone is sometimes inscribed), and is thought to be impossible to ever identify. Much work goes into trying to find a certain soldier, and to verify that it is indeed one of the relevant nation's soldiers.
Perhaps the first memorial of this kind in the world is the 1849 Landsoldaten ("Foot Soldiers") monument of the First war of Schleswig in Fredericia, Denmark. Another early memorial of this kind is the 1866 memorial to the unknown dead of the American Civil War.
Although monuments have been built as recently as 1982 in the case of Iraq, it is unlikely that any further ones will be constructed. Advances in DNA technology mean that even the tiniest fragment of bone is usually identifiable.
The monument is actually a cenotaph, the work of architect Emmanouil Lazaridis. A slain ancient warrior, sculpted by Fokion Rock, is depicted on the monument which is inscribed with a segment of Pericles' tribute to the dead of the Peloponnesian War. The names of places where battles have been fought by the Greek Army since 1821 are also inscribed on the monument. An honorary guard of two Evzones is always posted at the site.