Dacians indeed had warriors who wielded the two-handed falx with devastating effect on the Roman army as shown on the Tropeum Traiani.
Using the falx, the Dacian warriors were able to counter the power of the compact, massed Roman formations. During the time of the Roman conquest of Dacia (101-102, 105-106), legionaries had reinforcing iron straps applied to their helmets. The Romans also introduced the use of leg and arm protectors (greaves and manica) as further protection against the falxes.
Dacians used the falx and Thracians the rhomphaia since at least the 4th century BC!
http://en.wikipedia.org/wiki/Falx
The Dacian falx came in two sizes: one-handed and two-handed. The shorter variant was called sica (sickle) in the Dacian language.
The two-handed falx was a pole-arm. It consisted of a three-feet long wooden shaft with a long curved iron blade of nearly-equal length attached to the end. The blade was sharpened only on the inside, and was reputed to be devastatingly effective. However, it left its user vulnerable because, being a two-handed weapon, the warrior could not also make use of a shield. It may be imagined that the length of the two-handed falx allowed it to be wielded with great force, the point piercing helmets and the blade splitting shields - it was said to be capable of splitting a shield in two at a single blow. Alternatively, it might used as a hook, pulling away shields and cutting at vulnerable limbs.
The Thracians also made use of the falx. They also used the rhomphaia, a weapon very similar to the two handed falx but much less drastically curved.
The two handed falx is clearly related to the Thracian rhomphaia. It is a derivative of both the sword and the spear, having evolved from a spear to a polearm before becoming more drastically curved to facilitate a superior cutting action. This drastic curve rendered the falx as a purely offensive weapon to be used against a broken or routing force. Typically, an enemy would be broken by a sustained hail of missile fire from javelin, dart, bow, sling, and stone throwing troops before being chased down and cut to pieces by the falx wielding troops.
http://en.wikipedia.org/wiki/Rhomphaia
Most rhomphaias were polearms, featuring a straight or slightly curved single-edged blade attached to a pole that was considerably longer than the blade. Some rhomphaias had short handles that extended to only the length of the blade. Although the rhomphaia was similar to the falx, most archaeological evidence suggests that rhomphaias were forged with straight or slightly curved blades, presumably to enable their use as both a thrusting and slashing weapon.