the british museum library was the national library of the united kingdom in all but name. during panizzi's tenure as keeper of printed books its holdings increased from 235,000 to 540,000 volumes, making it the largest library in the world at the time. its famous circular reading room was designed and built by architect sydney smirke from a sketch drawn by panizzi. the new reading room opened in 1857. the british museum library formed the bulk of what became the british library in 1973 and the "round" reading room was in use until 1997 when the library moved to its current site at st. pancras.