Jamieson, Fausset and Brown on Acts 25:11

11. I appeal to Cæsar--The right of appeal to the supreme power, in case of life and death, was secured by an ancient law to every Roman citizen, and continued under the empire. Had Festus shown any disposition to pronounce final judgment, Paul, strong in the consciousness of his innocence and the justice of a Roman tribunal, would not have made this appeal. But when the only other alternative offered him was to give his own consent to be transferred to the great hotbed of plots against his life, and to a tribunal of unscrupulous and bloodthirsty ecclesiastics whose vociferous cries for his death had scarcely subsided, no other course was open to him.