Sometime in the Romantic era this instrument got its modern form and the technique progressed so much that cello gradually took a more soloistic place .
But the more virtuosistic the repertoire became less room there was for improvisation
Mid-17th century somewere in Europe this "Violone" (big violin) was born. its function? Playing and improvising on the "basso continuo" (pretty much the same job that a modern Double bass does today)