Pilum

[Templar Knight]

Could it be possible that after Roman Empire crumbled the use of this kind of weapons ended because Frankish and Gothik armies didnt have enough drill and dicipline to use them to same effect as Romans.

Thats a very good point - Im not really an expert on Frank/Gothic warfare but im not sure if their tactics would have allowed for the use of pilum type weaponry in terms of discipline as you have said.

[Uesugi Kenshin]

Pila would also have probably been expensive just on the materials side because they were made of iron.

BTW Kagemusha GREAT sig!

[Krusader]

In the 3rd-5th centuries the Roman Empire had too few men to defend the empire itself, so army service was made compulsory, which was an unpopular move, and seems to might have been abolished at a later date.
Many barbarians were recruited into the Roman army in the 4th century, and this led to a "barbarization" of the Roman army. The barbarians continued to fight in their style, which seems to not have included the pila.
One possible theory

This is based on what I've read in a military book about ancient warfare and my curriculum at Uni

[Krusader]

Btw, the almogavares used a variant of the pilae during the Middle Ages.

http://en.wikipedia.org/wiki/Almogavares

They were highly efficient and Aragon used them frequently.

[Kagemusha]

Thanks Krusader!
Woderfull!So Pilum never really died out like i thought before.
Isnt it kind of nice too see that Legion like troops beated Knight Army.
This is very intresting.