At that time Samuel died. Saul, when the Philistines made war upon him, consulted God, and no answer was returned to him. Then, by means of a woman whose entrails a spirit of error had filled, he called up and consulted Samuel. Saul was informed by him that on the following day he with his sons, being overcome by the Philistines, would fall in the battle. The Philistines, accordingly, having pitched their camp on the enemy's territory, drew up their army in battle array on the following day, David, however, being sent away from the camp, because they did not believe that he would be faithful to them against his own people.
But the battle taking place, the Hebrews were routed and the sons of the king fell; Saul, having sunk down from his horse, that he might not be taken alive by the enemy, fell on his own sword. We do not find any certain statements as to the length of his reign, unless that he is said in the Acts of the Apostles to have reigned forty years. As to this, however, I am inclined to think that Paul, who made the statement in his preaching, then meant to include also the years of Samuel under the length of that king's reign. Most of those, however, who have written about these times, remark that he reigned thirty years.
I can, by no means, agree with this opinion, for at the time when the ark of God was transferred to the town of Cariathiarim, Saul had not yet begun to reign, and it is related that the ark was removed by David the king out of that town after it had been there twenty years. Therefore, since Saul reigned and died within that period, he must have held the government only for a very brief space of time. We find the same obscurity concerning the times of Samuel, who, having been born under the priesthood of Eli, is related, when very old, to have fulfilled the duties of a priest.
By some, however, who have written about these times (for the sacred history has recorded almost nothing about his years), but by most he is said to have ruled the people seventy years. I have, however, been unable to discover what authority there is for this assumption. Amid such variety of error, we have followed the account of the Chronicles, because we think that it was taken (as said above) from the Acts of the Apostles, and we repeat that Samuel and Saul together held the government for forty years.
Source: Sacred History (New Advent)