Early in the year 343 we find Athanasius had travelled, via Rome, from Alexandria, North Africa, to Gaul; nowadays Belgium / Holland and surrounding areas, where Hosius of Cordoba was Bishop, the great champion of orthodoxy in the West. The two, together, set out for Sardica. A full Council of the Church was convened / summoned there in deference to the Roman pontiff's wishes. The travel was a mammoth task in itself. At this great gathering of prelates, leaders of the Church, the case of Athanasius was taken up once more, that is, Athanasius was formally questioned over misdemeanours and even murder, (a man called Arsenius and using his body for magic, – an absurd charge.). [The Council was convoked for the purpose of inquiring into the charges against Athanasius and other bishops, on account of which they were deposed from their sees by the Semi-Arian Synod of Antioch (341), and went into exile. It was called according to Socrates, (E. H. ii. 20) by the two Emperors, Constans and Constantius; but, according to Baronius by Pope Julius (337–352), (Ad an. 343). One hundred and seventy six attended. Eusebian bishops objected to the admission of Athanasius and other deposed bishops to the Council, except as accused persons to answer the charges brought against them. Their objections were overridden by the orthodox bishops, about a hundred were orthodox, who were the majority. The Eusebians, seeing they had no chance of having their views carried, retired to Philoppopolis in Thrace, Philippopolis (Thracia), where they held an opposition council, under the presidency of the Patriarch of Antioch, and confirmed the decrees of the Synod of Antioch. ]. Once more, at the Council of Sardica, was his innocence reaffirmed. Two conciliar letters were prepared, one to the clergy and faithful of Alexandria, the other to the bishops of Egypt and Libya, in which the will of the Council was made known. Meanwhile, the Eusebian party had gone to Philippopolis, where they issued an anathema against Athanasius and his supporters. The persecution against the orthodox party broke out with renewed vigour, and Constantius was induced to prepare drastic measures against Athanasius and the priests who were devoted to him. Orders were given that if the Saint attempt to re-enter his see, he should be put to death. Athanasius, accordingly, withdrew from Sardica to Naissus in Mysia, where he celebrated the Easter festival of the year 344. It was Hosius who presided over the Council of Sardica, as he did for the First Council of Nicaea, which like the 341 synod, found Athanasius innocent. &. He celebrated his last Easter in exile in Aquileia in April 345, received by bishop Fortunatianus.
With whom did Athanasius travel to Sardica?
Hosius of Cordoba