The Roman Gladius Sword
The Gladius is a short sword equally effective at chopping and thrusting. It has a wide, heavy blade making it capable of severing limbs and heads, and an acute point designed to penetrate armor, bone, and flesh. The Gladius was adopted from a Celtic sword type first encountered in Spain. When the Roman Army first used it in a major battle against Macedonians, the results were impressive. Classical witnesses reported a profound effect on the Macedonians morale, and claim the battlefield was strewn with their severed arms and heads.
The primary attack mode of the Gladius was to thrust. The Gladius was an integreated part of the Roman fighting system. It was used in conjuntion with the Pila (special armor piercing / shield incapacitating javelin) and Scutum (large, light Roman shield) as well as the iron or brass helmets and iron body armor (mail shirts originally, later vests of metal bands)
Fighting in formation, Roman Legionaires used to alternate between charging disorganized opponents in small blocks of 60 or 120 men, and holding fast with their shields interlocked into a testuodo (turtle) to withstand missiles of their enemies. The Gladius has been described by many as the perfect sword. Certainly for the type of close in fighting the Romans specialised in, it was hard to beat. One on one out in the open however, against a barbarian armed with a longer cutting sword, the Roman Legionaire was even with his huge shield, at something of a disadvantage with his short though dangerous gladius.
Still, personally, if I was going to keep a sword behind the seat of my car for personal protection (not that this is advised for both legal and technological reasons!) it would probably be the Gladius.
