One of the most interesting problems in the political history of the last three decades of the third century B.C. is the appearance of the Romans east of the Adriatic. Whether Rome in the First and Second Illyrian Wars was inaugurating a definite imperialistic policy with the conscious aim of gaining control in the Balkan peninsula, or whether at this time she was acting purely on the defensive against Illyrian piracy, are questions with which I am not concerned at present. The fact of primary importance is that, by establishing herself in Illyria, Rome came into contact with Macedon, and this contact was bound to lead to hostilities; for the Antigonids could not fail to resent the intrusion of a stranger in what they considered their own sphere of influence. In this paper I propose to consider the attitude of Philip V to the Roman protectorate in Illyria at the beginning of his reign. Since his whole life was one long struggle with Rome, the importance of understanding his policy in regard to this question is obvious. Before entering upon the subject, however, it will be necessary to try to determine how far westward Macedonian authority extended. A knowledge of this western frontier will not only inform us on the proximity of Macedonian possessions to the Roman protectorate, but will also reveal some of the problems which the barbaric Illyrian and Dardanian tribes presented to Philip in this quarter. Once we have these matters clearly in mind, we shall be in a much better position to form an unbiased estimate of Philip's attitude to what may be called his Illyrian problem.