spawning urdf in gazebo_ros

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Does anyone know how to spawn a simple urdf box in gazebo? I want to spawn an entire robot but the gazebo tutorials on this have a bit complicated launch files and use complicatted .xacro robots. I'm on a beginner level, my simple robot is just .urdf not even using .xacro.

A box like this!

 <robot name="origins">
<link name="base_link">
    <visual>
        <geometry>
            <box size ="8.8 0.4 2"/>
        </geometry>
    </visual>
    <collision>
        <geometry>
            <box size ="8.8 0.4 2"/>
        </geometry>
    </collision>
        <inertial>
                <inertia ixx="0.0" ixy="0.0" ixz="0.0" iyy="0.0" iyz="0.0" izz="0.0"/>
        <mass value="0.1"/>
        </inertial>
</link>


</robot>

I'm trying to use the command rosrun gazebo_ros spwan_model but it just says:

Loading model xml from file

Waiting for service /gazebo/spawn_urdf_model.

Nothing more happens...

Any ideas?