Ancient fortifications in Central Ukraine

[Domen]

I've never heard of it before, pretty intriguing though (the "Great Wall of Ukraine"):

It was a system of fortifications (in total 2000 kilometers of defensive walls) built over long time from the 2nd century BC to the 7th century AD:

http://uk.wikipedia.org/wiki/Змієві_вали

It seems that they were built to protect people living in Northern Ukraine from invasions by steppe nomads of Southern Ukraine and Russia:

There was a formidable system of ancient military fortifications called Serpent's Wall protecting fertile regions of forest steppe against the intrusions from the steppe. The ancient walls were built between the 2nd century BC and 7th century AD, according to carbon dating. Height 10-15 m. Total length is around 2000 km. This shows the scale of military operations of those times.

Map showing this system of walls (or maybe various walls not related to each other?):



Reconstruction of wooden structures:



Modern remains (mostly ground, wood burns and decays):









Arrowheads discovered there: