Bridge to Xenothi [Survival]

Invaders are closing in on the capital, Xenothi. Defend the bridge to the city as waves of ever increasing difficulty try and destroy the final pillar of hope on New Terra. Prevent the invaders from establishing a foothold within the city long enough for reinforcements to arrive. This is a survival map, the second phase for this level will be made available in another map in which you will prepare a counter attack.