There are perilously few composers of whom you could reliably expect to say, after a long day of total immersion in their music, that they were really as great as you thought. Beethoven, however, could well be the greatest - an impression confirmed by hearing all the works he wrote for cello and keyboard in one epic day, courtesy of Steven Isserlis and Robert Levin.

What was most striking was how strong Beethoven's envelope-pushing tendencies were. The three sets of variations heard in the morning, alongside his own transcription of his Horn Sonata, transcended the potential limitations of the form.

In the afternoon and evening, we heard the five Cello Sonatas; works that span the whole of Beethoven's career, and that show even less regard for convention. The first two, Op 5, threw Levin into the virtuoso spotlight; the middle-period Sonata No 3, Op 69, brought some of the day's most haunting moments as Isserlis caught perfectly the captivating melancholy of the opening. But it was the final work, Op 102, No 2, that brought the greatest introspection with the first genuine slow movement of the day, thrown into sharp relief by the exhilarating finale.

Levin was on scintillating form, getting a surprising range of colour from his instrument, a copy of an early 19th-century fortepiano. In the morning, it seemed to need tuning every five minutes but, mercifully, it settled down. As for Isserlis, this was surely one of his finest performances.