During a few games of Capture the Flag, trends quickly emerged. Skilled players would surround the flag with walls, supply bunkers (Brimming with explosives!), and turrets. With enough Rift Energy, certain structures can benefit from real-time upgrades, like turning a static wall into a motion-activated gate that drops into the ground at the presence of friendly troops but rockets back up when trouble starts brewing.
My favorite structure comes in the form of a powerful laser tower, which invokes War of the Worlds with gusto. Battles really come to life when shafts of destruction streak across the battlefield and incinerate the opposition. These towers automatically target the opposing team when vacant, but you can climb in and man the tower yourself if you want more hands-on time with the carnage.
Some of the available structures can deploy on top of pre-existing structures. Certain walls, for example, have slots on top that accommodate extra turrets. This gives you the opportunity to fortify certain positions with even more defenses, especially if you see the enemy team continuously approaching from one angle.