Lantean beam cannon

The Lantean beam cannon was a highly advanced energy weapon built by the Ancients and used on their defence satellites 10,000 years ago.

It is possibly the most powerful energy weapon ever built, more powerful than the quantum phasers, the only weapon that may match it are the Ori weapons.

Overview
Similar to the quantum phasers the beam cannon fires a beam of green/yellow energy of some form capable of easily destroying a Wraith Hive ship in a single shot. (SGA "The Siege, Part 1")

In terms of effectiveness the beam cannon is highly effective, even the quantum phasers take three shots to destroy a Wraith Hive and massive numbers of drones to accomplish the same and this was while powered by a Naquadah generator instead of the Ancient power source. (SGA: "The Last Man", "No Man's Land")

History
It is unknown if the Ancients used these weapons elsewhere than the Lagrangian satellite network used to defend Lantea's solar system.

More than 10,000 years ago when the Ancients fortified Lantea they built a network of satellites armed with these weapons.

During the First siege of Atlantis they where used to defend Atlantis, however they proved not to be enough, eventually all but one of the satellites was destroyed. (SGA: "The Siege, Part 1", "The Defiant One")