Zevachim 108: Slaughtering/Offering on an Altar or Not

We learn a new Mishna:

• slaughtering outside the Temple courtyard is worse than offering up outside
• this is because one who slaughters an offering outside of the Temple courtyard even for an ordinary purpose (not for G-d's sake) is liable but offering outside of the Temple courtyard is exempt
• offering outside is treated with stringency because two people who hold a knife and slaughter together outside are exempt, while those who grasp a limb from an offering and offer it together outside the courtyard, they are liable
• if one offers up part of an offering outside the courtyard in error and then offered other parts of the offering, s/he must bring a sin offering for each act of offering up 
• This is debated by Rabbi Shimon and Rabbi Yosei
• They also discuss the consequences when there may have been an altar - even a rock or a stone - built outside of the Temple courtyard

Rabbi Yosei adds: And one is liable  for offering up an offering outside  the courtyard only once he offers it up at the top of an altar that was erected there. Rabbi Shimon says: Even if he offered it up on a rock or on a stone,  not an altar, he is liable.  The notion of an altar; something 'higher', is significant as a marker of spiritual importance.