What is the ruling on establishing special cemeteries for martyrs and burying them therein, and what are the evidences for that?

The Sunnah dictates that martyrs should be buried where they were killed, a practice affirmed by the jurists of the four madhhabs, just as the Prophet (peace be upon him) and his Companions did. It is reported from Ibn al-Qayyim that the Prophet (peace be upon him) ordered the return of the martyred Companions who had been transported to Madinah, so they could be buried at their places of death. There is no harm in establishing a cemetery for all the martyrs of a battle at the locations where they were killed. However, establishing a general cemetery for all martyrs has no basis in the Sunnah.