The overall size of the Roman forces in Roman Britain grew from about 40,000 in the mid 1st century AD to a maximum of about 55,000 in the mid 2nd century. the proportion of auxiliaries in Britain grew from about 50% before 69 AD to over 70% in c. 150 AD. By the mid-2nd century, there were about 70 auxiliary regiments in Britain, for a total of over 40,000 men. These outnumbered the 16,500 legionaries in Britain (three Roman legions) by 2.5 to 1. This was the greatest concentration of auxilia in any single province of the Roman Empire. It implies major continuing security problems; this is supported by the (thin) historical evidence. After Agricola, the following Emperors conducted major military operations in Britain: Hadrian, Antoninus Pius and Septimius Severus.