HILARIUS or HILARUS (d. 468), bishop of Rome from 461 to 468, is known to have acted as legate of Leo the Great at the "robber" synod of Ephesus in 449. There he so vigorously opposed the condemnation of Flavian of Constantinople that he was thrown into prison, whence he escaped to Rome. He was chosen to succeed Leo on Nov. 19, 461. In 465 he held at Rome a council which put a stop to some abuses, particularly to that of bishops appointing their own successors. His pontificate was also marked by the extension of papal authority in France and Spain. Hilarius died on Nov. 17, 467.