By base lighting I mean natural lighting; for this scene it is the moon and its bounce light. The moonlight in this image is very important, I used it to help focus the viewer's eye into the centre of the image and help create depth. I didn't want the moon itself to be visible as I thought it would interfere with the composition of the image, so I kept it hidden behind the buildings. I placed a MR-Area Omni light just behind the archway, about halfway up the stairs. I used the attenuation settings to give me more control over the falloff of the light so it starts and ends when I tell it to. You can achieve this control by editing the attenuation settings and adjusting the start and end values.
Here are the settings I used for the moon light (Fig.03).
Here is an image of the placed light (Fig.04).
I also added moon light to the upper right of the image using a MR_Area Spotlight. I gave it a white with a light blue tint and a power of 2.0 I positioned it so it was pointing across the surface of the wall; this also gave me a soft shadow from the roofing tiles and helped to pick out the bump map giving more detail to the image.