Pressures from beyond the empire’s border consumed the reign of Constans, grandson of Herakleios by his son Herakleios Constantine. He organized the Anatolikon and Opsikion themes in Asia Minor against the Arabs, who continued to tear away at imperial possessions. His military leadership did not meet with universal success, however: he was defeated at the battle of Phoenix in 655 and was forced to accept peace treaties in 651 and 659 with the great Arab general Mu’awiya. He had more success against the Slavs, invading Sklavinia in 658. He landed in Italy, campaigned against the Lombards, was the last emperor to visit Rome, where he confiscated the bronze roof from the Pantheon, and settled in Sicily. By increasing taxes and confiscating church property, he made himself unpopular with the local lay and ecclesiastical elites, as he did with the Church of Rome when he declared the independence of the archbishop of Ravenna. Constans failed to find common Christological ground between Monophysites and Chalcedonians, and exacerbated tensions with the West with his Typos, which forbade discussion of energies or wills, which were at the foundation of previous attempts at accommodation (Monoergetism and Monotheletism). Constans further alienated the western Church by arresting and exiling the pope in 653. His reign ended when he was murdered in his bath in Syracuse, either by a servant or a group of conspirators, and his body was returned to the capital by his eldest son, Constantine IV.
The design of Constans’s seals follows many of the design trends begun by his grandfather Herakleios: Constans can be seen aging on his seals and he demonstrates his dynastic continuity by associating his sons with him. There are four phases to Constans’s seals. Early in his reign Constans is shown beardless en buste, as he is on the coinage. Later (647–51) he is shown standing and with a progressively longer beard. In the third (654–59) and fourth (663–68) phases his sons Constantine, Herakleios, and Tiberios are added to the seals. Constans’s seals, adhering fairly closely to the design and inscription used by his grandfather, are more conservative than his coinage, which was output on a massive scale, and the copper denomination of which included the inscription “ἐν τούτῳ νίκα,” a reference to Constantine’s vision of the cross at the Milvian Bridge. For the full range of Constans's seals see the Herakleian Dynasty in the Dynasties of Empire section.