Fixing a gate

[Zymon]

Can anyone help a novice? I have a garden wall built with an opening for a gate. The gate will be raised three concrete blocks high with steps up to it. This is because the garden on one side of the wall is higher than the other. Should I fix gate posts directly to the concrete block wall so they sit on the wall or put them behind the wall and sink them to the depth of the wall three concrete blocks down?