fallen battle cross
Anzac soldiers had been buried in a special grave.
The government does supply grave markers for those killed in action. There is typically not a cost for this.
unknown soldiers
It would have been called a ditch. World War I was starting in 1914 and large ditches played a major part in the land warfare. The were called "Trenches" and the soldiers who occupied them described them as a grave with both ends kicked out.
because they may have been blown up, or lost.
An anonymous burial is one in which the grave site has only a simple marker to show it is there. The grave remains unmarked with a name or date. Some examples of an anonymous burial include a simple cross or a rifle and helmet.
It's generally called an epitaph.
Ghoul
Writing on an grave stone is called an epitaph.
Eventually they were buried in a graveyard for the soldiers. The body parts were put in a mass grave unless they knew who it came from. See answer below on the related link.
montana
china