Excerpts from Books and Wikipedia
"Because he was afflicted with a limp and slight deafness due to sickness at a young age, his family ostracized him and excluded him from public office until his consulship, shared with his nephew Caligula in 37. Claudius's infirmity probably saved him from the fate of many other nobles during the purges of Tiberius's and Caligula's reigns; potential enemies did not see him as a serious threat. His survival led to his being declared emperor by the Praetorian Guard after Caligula's assassination, at which point he was the last man of his family. Despite his lack of experience, Claudius proved to be an able and efficient administrator. He was also an ambitious builder, constructing many new roads, aqueducts, and canals across the Empire. During his reign the Empire began the conquest of Britain (if the earlier invasions of Britain by Caesar and Caligula's aborted attempts are not counted)." [Wikipedia]