Bricks, Masonry, Asphalt and Concrete - Ret.wall question

I am building a fire pit with seating(ret.walls) out of large and small limestone pieces. Large as in need dolley. I have read everything from needing conc. footing to tampered gravel base. I was set on the conc. footing thing until I saw a similiar design at a local strip mall and they mortared the wall and there doesn't appear to be any footing at all. I live in central Texas and we are basically on rock. I am using the exact material that the strip mall is. Should I use the stronger Type S(i think) mortar. Everything I have read leads me to a conc. footing when mortaring, but I am confused why the strip mall didnt do this. I inspected wall for about an hour and see no evidence of even a gravel base. Also, any recommendations for mortaring a field stone wall would be appreciated. I have done numerous walls with chopped block, but never random like this. I am using very heavy pieces in there. Oh, the strip mall is hubbed by Costco and they are definetly not doing anything on the cheap there. The wall is awesome and very sturdy. Thanks for any input.