The Greek Revival façade facing Great Russell Street is a characteristic building of Sir Robert Smirke, with 44 columns in the Ionic order high, closely based on those of the temple of Athena Polias at Priene in Asia Minor.
In 1846 Robert Smirke was replaced as the Museum's architect by his brother Sydney Smirke, whose major addition was the Round Reading Room 1854-1857; at 140ft in diameter it was then the second widest dome in the world, the Pantheon in Rome being slightly wider.