Another word for unconquerable

Baxter was possessed by an unconquerable belief in the power of persuasive argument.

In spite of all, the dominant fact remains, that to the end he was zealous for his God and for the salvation of his people, nay, of the whole of humanity, and that he never lost the unconquerable certainty of his divine mission.

His unconquerable valour gained him many followers, and he defeated an army sent against him by the Kajars in 1792.

His image was carried in the pompa circensis amongst those of the immortal gods, and his statue set up in the temple of Quirinus with the inscription "To the Unconquerable God."

But the unfortunate prince had to choose between dependence and extermination, for his unaided resources were powerless against the persistent attacks of the unconquerable The Prussians.