What's in a name? Longsword, bastard sword, and hand-and-a-half sword are all names used to describe a variety of medieval European swords. The names derive from words popular at different times and places. For example, 'longsword' is related to the German 'langshwert', and 'bastard sword' from the French 'épée bâtarde', but they all refer to the same basic form, a double edged sword with a grip large enough to be used with two hands. Functionally, swords become more maneuverable, powerful, and fast when the handle is gripped with two hands. We see these depicted in art beginning in late antiquity and the early Middle Ages...
Miniature from Stuttgart Psalter, Ps 143, 10, showing David and Goliath. First quarter of the 9th c. A.D. (Stuttgart: Wurt. Landesbib. Folio 158 v.).
Some of the earliest swords seemingly designed for two handed use are the “Grete Swords of War” of the 13th C. These are referred to by a variety of names and include Langschwert, spadone or spada longa, grootzwaard, épée bâtarde, and bastard sword. These are all in reference to swords commonly called hand and a half swords or longswords today. The earliest forms of these are oversized examples of the single handed swords would be hard to distinguish as a separate group. When we see references to the Grans espées d'Allemagne (large swords of Germany) at the beginning of the 14th century, it is obvious that the idea of a larger sword for use with two hands has entered the arsenal of the Medieval Knight.
Early depictions of a sword in two hands show swords such as the A&A Hungarian Sword used to deliver these blows.
Cod. Pal. germ. 848 Große Heidelberger Liederhandschrift (Codex Manesse) Zürich, 1305 bis 1340 321v: Herr Dietmar der Setzer
The evolution of the large swords of war into the Knightly longsword can first be seen as a distinct group in the swords of Oakeshott’s Type XIIa and XIIIa. These swords are distinctly made for use in one or two hands and have the grip length and reach to be used as longswords as described in the material from the Liechtenauer tradition and Fiore de Libre. The evolution of these swords and how they were used was a dynamic and vigorous interplay of weapons and armor development with the keenest minds of martial combat striving to define the new environment of plate armor and longsword.
The specific term used to describe these swords in period varied by region as listed above. The intention of how to use the sword most likely dictated the way they were listed in inventories of the day. It was not defined, as we do today, by specific lengths or forms. A sword called by these names would most likely have a blade length of 33 to 40+ inches and a grip and pommel that one can get both hands placed comfortably upon. This could be a 5-inch handle with a pommel that accommodates being used as part of the grip to one that would have considerable room between the hands. The distance between the hands obviously increases the leverage that combatant could exert on the weapon. The variety of longswords that have survived are diverse and it is obvious that personal preference and intended use where important factors in what a warrior of the period would choose to use.
Over the next several centuries blade shapes varied but we see these swords in two hands being used across the Europe. Some had broad parallel edges to those with acute tapers from the guard to a spike like point and many variations in between. The cross sections of the blades also varied a great deal. We see very thin blades with tremendous cutting potential to swords of the more common diamond cross section, many with fullers, to the category of Tucks which had blades designed for thrusting and levering ones opponent in close play. All of these types can be classified in some of their forms as Longsword, Bastard Sword and Hand and a Half swords.
Modern replica longswords cover many of these diverse types, though certain styles are less well represented in the current market place. This probably represents the differing tastes of current sword buyers from those of the Middle Ages. As an example, the Type XIX blade cross section are not as common as they seem to be in the surviving historical examples, and the tuck style blade is rarely seen at all in modern production and is often only done as a custom order.
Regardless of what they are called these swords are all of a type that is iconic to the middle ages.