Rufio was the son of a freedman and came in 48 BC as a member of Caesar's army to Egypt. After Caesar had intervened in the Ptolemaic struggle for the throne between the siblings Cleopatra and Ptolemy XIII and won the Alexandrian war against the party of Ptolemy XIII (January 47 BC) he stationed three legions in Egypt to safeguard his victory. These troops, the 27th, 37th, and 39th legion, served to protect, but also to check the rule of Cleopatra, who had become Caesar's mistress and now reigned as allied queen.