how can I batching textures?

I'm creating a 2D game based on a tilemap and I have some problems with the performance. Each tile has dimensions of 16x16 then in a screen of 1900x1080 pixels are rendered large quantities of tiles. When I start the game in the statistics it says 'Draw Calls: 12000 Saved by batching: 0'. I read something about the Draw Call Batching but I can not figure out how to make it work. I draw my tile map in this way:

    public List<Texture2D> ObjSprite = new List<Texture2D>();
     ObjSprite.add("blabla");
     ...
     
     //Draw World
     for (int y = 0; y < TerrainMap.GetLength(0); y++) //Y
     {
     for (int x = 0; x < TerrainMap.GetLength(1); x++)//X
     {
     //Draw Wall
     float light = 0.05F;
     Graphics.DrawTexture(new Rect(x * 16, y * 16, 16, 16),WallSprite[Tindex],new Rect(0,0,16,16),8,8,8,8,new Color(light,light,light));
     }
     }
 

How Can I minimize Draw Calls?? Sorry for my bad english.