Darth Maul fabricated his double-bladed lightsaber out of necessity. Sent to the Jentares system to assassinate the reclusive Jedi master, Siolo'urmanka, Maul found himself unable to physically compete with the warrior. Their initial bout ended with Maul being batted across the face with his enemy's staff and then disarmed. Knowing that he couldn't beat his opponent through martial prowess, Maul fell back on his strategic know-how, resolving to surprise his opponent.[1]

Returning to his ship, Maul drew on Sith schematics he had at his disposal, fabricating two separate lightsabers. Welding the weapons together, Maul created his new lightsaber.[1] As Maul's lightsaber was composed of two weapons with connected pommels, they both possessed identical designs. Directly below the beam emitter and projection plate of both weapons was the modulation circuitry and the activator. Next to the activator was a control lock and a small, ridged handgrip. The next control was for blade modulation, with a second set of control locks directly below it. The center of the weapon was the joint between the two lightsabers.[2]

Maul took considerable pride in the fashioning of the crystals for his weapon. Creating a set of four Synthetic lightsaber crystals in a compression furnace, he went into deep meditation for four days, using the Force to control and monitor the formation of the crystals.[3]

Source: Starwars.wikia.com