Antoninus Pius ( Titus Aurelius Fulvus Boionius Arrius Antoninus , 19 September 86 â `` 7 March 161 ) , or simply Antoninus , was Roman Emperor from 138 to 161 . Titus Aurelius Fulvus Boionius Arrius Antoninus ( 19 September 86 â `` 7 March 161 ) , commonly known as Antoninus or Antoninus Pius , was Roman Emperor from 138 to 161 .