What instruments in a chamber orchestra typically provides the harmonic underpinning for other melodic instruments but can carry the principal melody on their own as well?

In a chamber orchestra, the string instruments, particularly the viola and cello, typically provide the harmonic underpinning while also having the ability to carry the principal melody. The viola often adds depth and warmth to the harmony, while the cello can deliver both harmonic support and lyrical melodies. Together, they create a rich texture that enhances the overall sound of the ensemble.