Complex sentence: Veliko Tarnovo is one of the oldest settlements in Bulgaria, having a history of more than five millennia, as the first traces of human presence dating from the 3rd millennium BC are on Trapezitsa Hill.
Split into simpler sentences: Veliko Tarnovo is one of the oldest settlements in Bulgaria, with a history of more than five millennia. The first traces of human presence, dating from the 3rd millennium BC, were discovered on Trapezitsa Hill.