The Mishna deals with a situation where a person comes upon a place where he finds a body buried, and it is not clear whether this was a body that was buried here temporarily, with the intent of moving it to a proper cemetery when the opportunity arose, or if it is part of a shekhunat kevarot – a formal burial area – that cannot be disturbed. Such a discovery was likely to take place during the period before one of the shalosh regalim – the three pilgrimage holidays, Pesaḥ, Shavu’ot and Sukkot – when it was common practice to check the roads that the olei regalim – the pilgrims – would take in order to assure that they were clear of anything that would ritually defile them. The olei regalim would always need to remain in a state of ritual purity in order to bring sacrifices in the Temple, and it was, therefore, essential that the roads were kept clear of tum’ah on their behalf. Thus, discovering a dead body on or near the public thoroughfare led to the question “can this body be moved?”
Generally speaking, halakha recognizes that met koneh et mekomo – that a dead person takes possession of the ground where he is lies and cannot be moved. Therefore, if we have reason to believe that a person was buried in a specific place, he cannot be moved, and the grave would need to be clearly marked. If, however, an unknown body was found, the Mishna teaches that it can be moved to a cemetery. One case where we are forced to assume that a body was buried in a place purposefully is when a number of bodies were found buried in close proximity, and another one is found nearby (within twenty amot), since raglayim la-davar – the status quo would indicate that this is a shekhunat kevarot.