From Marion Zimmer Bradley’s Mists of Avalon: Gwenhwyfar persuades Arthur to put aside the Pendragon Banner

Arthur came that night to her chambers, just as she set the last stitches to it, and the women were lighting the lamps.
“How is it with you now, my dear one? I am glad to see you up again and well enough to work,” he said, and kissed her. “Dearest, you must not grieve so…no woman could bring a healthy child to birth under this strain, with the battle impending at any moment--I should have sent you to Camelot, indeed. We are young still, my Gwenhwyfar, God may yet send us many children.” But she saw the vulnerable look on his face, and knew he shared her sorrow.
She clasped his hand and drew him down beside her on the bench where she sat before the banner. “Is it not fair?” she said, and thought she sounded like a child begging for praise.
“It is very beautiful. I thought I had never seen so fine work as this”--and he laid his hand on the crimson-worked scabbard of Excalibur that never left his side--”but this is finer still.”
“And I have woven prayers for you and your Companions into every stitch,” she said, in entreaty. “Arthur, listen to me--do you think, could it not be, God has punished us because he feels we are not fit to give this kingdom another king, you and I, unless we will vow ourselves to serve him faithfully, not in pagan ways but in the new way under Christ? All the forces of pagan evil are allied against us, and we must fight it with the cross.”
He laid his hand over hers and said, “Come dear love, this is folly. You know I serve God as best I may…”
“But you still raise that pagan banner of serpents over your men,” she cried, and he shook his head in distress.
“Dear love, I cannot break faith with the Lady of Avalon who set me on my throne--”
“It was God, and no other, who set you on your throne,” she said earnestly. “Ah, Arthur, if you love me, do this, if you wish for God to send us another child! Do you not see how he has punished us by taking our son to himself?”
“You must not speak so,” he said firmly. “To think God would do so is superstitious folly. I came to tell you at last the Saxons are massing, and we shall move to give them battle at Mount Badon! I would now that you were well enough to ride to Camelot, but it cannot be--not yet--”
“Ah, I know it well, I am only an encumbrance to you,” she cried out bitterly. “I was never more to you--it is a pity I did not die with my babe.”
“No, no, you must not speak so,” he said tenderly. “I have every confidence that with my good sword Excalibur and all my Companions, we shall triumph. An you must pray for us night and day, my Gwenhwyfar.” He rose and added, “We will not march till daybreak. I will try to come and take leave of you tis night before we march, and your father too, and Gawaine and perhaps Lancelet--he sent you greetings, Gwenhwyfar, he was very troubled when he heard you were so ill. Can you speak to them if they come?”
She bent her head and said bitterly, “I will do my king and my lord’s will. Yes, let them come, though I wonder you trouble to ask my prayers--I cannot even persuade you to put away that pagan banner and raise the cross of Christ…And no doubt God knows you rheart, since God will not let you ride forth into battle believing that any son of yours shall rule this land, because you have not yet resolved to make this a Christian land…”
He stopped and let her hand go, and she could feel him looking down at her. At last he bent and put his hand under her chin and raised her face to look at his. He said quietly, “My dear lady, my own dear love, in God’s name, believe you that?”
She nodded, unable to speak, wiping her nose like a child on the sleeve of her gown.
“I tell you, dear lady, before God, I believe it not, that God works in such ways, nor that it matters so much what banner we carry. But if it matters thus to you--” He paused and swallowed. “Gwenhwyfar, I cannot bear to see you in such distress. If I bear this banner of Christ and the Virgin into battle over my troops, will you cease to mourn, and pray to God for me with your best heart?”
She looked up at him, transformed, her heart lifting with a wild joy. Would he indeed do this for her? “Oh, Arthur, I have prayed, I have prayed--”
“Then,” said Arthur, with a sigh, “I swear it to you, Gwenhwyfar-- I shall carry only your banner of Christ and the Virgin into battle, and no other sign shall be raised above my legion. So bit it, amen.” He kissed her, but Gwenhwyfar though he looked very sad. She clasped his hands and kissed them, and for the first time, it seemed that the serpents on his wrists were nothing, mere faded pictures, and that she had indeed been mad to think they could have power to harm her or her child.