Two-handed Sword +1 is an enchanted weapon. When this sword is compared to the standard two-handed sword, it has +1 bonus to THAC0, damage and speed factor. At 12 lbs it is also 3 lbs lighter. The item value is in Baldur's Gate 1500, but 900 in Baldur's Gate II.
Dropped by seven skeleton warriors, which are quite powerful and may only be found in Durlag's Tower or in two areas which can only be accessed during the last chapter of the game. (Three of these skeletons are at the first underground floor of Durlag's Tower. The other four are spread evenly in the last two available areas.)
The two handed sword is a derivative of the long sword. Weaponsmiths have always looked for ways to improve existing weapons. In an effort to improve the long sword, the blade was lengthened. Eventually, the handle had to be extended and two hands became necessary to properly swing the sword. The primary function of two-handed swords is cleaving mounted knights and breaking up pike formations. This one has been enchanted with a few magical properties.