In the Ground

It is a mitzva d’oraisa to bury a meis in the ground, as the posuk says, “כי קבור תקברנו .” One who just puts a meis into a coffin or the like without burying him in the ground disregards the mitzva of kevura and also violates the issur of לא תלין (סנהדרין מו:, שו''ע יו''ד שסב א ).