The Greek Revival façade facing Great Russell Street is a characteristic building of Sir Robert Smirke, with 44 Ionic columns, 13.7 meters high, closely based on those of the temple of Athena Polias at Priene in Asia Minor. The pediment over the main entrance is decorated by sculptures by Sir Richard Westmacott depicting The Progress of Civilization, consisting of fifteen allegorical figures, installed in 1852.
from:
http://www.newworldencyclopedia.org/entry/British_Museum#The_Building(Sandy comprehensively beat me to it! I was too busy reading the rest of the article. Interesting stuff. I've never been to the British Museum, and it's now on my to do list)