In 1910 he joined the Department of Printed Books of the
British Museum. In 1909 and 1914, showing his interest in Roman history, he published two books on the subject. During the
First World War, worked for the
Postal Censorship Bureau. At the close of hostilities he returned to his work at the British Museum and his attention carried him towards the study of antique coins. From 1912, Harold Mattingly was a member of the
Royal Numismatic Society. He completely revised the chronology used for the study of Roman coins. He was awarded the
medal of the Royal Numismatic Society in 1941. He also translated
Tacitus' works
Agricola and
Germania. These two translations were published together in 1948 by Penguin Books under the title
Tacitus on Britain and Germany. 27,000 copies of this book were sold in that year. It was reprinted in 1951, 1954, 1960, 1962, 1964 and 1965. The second edition, revised by S A Handford, was published in 1970 under the title
The Agricola and the Germania. The book was revised again in 2009 by J B Rives. Mattingly's translation is considered one of the best and is still used (albeit in edited format) today. ==Personal life==