This system of co-rule would be the norm for most of the rest of the Ptolemaic dynasty. The co-rule was inaugurated by an amnesty decree and a royal visit to Memphis to celebrate the Egyptian new year festival. Ptolemy VIII was not satisfied with Cyrenaica and went to Rome in late 163 or early 162 BC to request help. The Senate agreed that the division was unfair, declaring that Ptolemy VIII ought to receive Cyprus as well. Titus Manlius Torquatus and Gnaeus Cornelius Merula were sent as envoys to force Ptolemy VI to concede this, but he procrastinated and obfuscated. On their return to Rome at the end of 162 BC, they convinced the Roman Senate to abandon their alliance with Ptolemy VI and to grant Ptolemy VIII permission to use force to take control of Cyprus. The Senate offered him no actual support in this endeavour and Cyprus remained in Ptolemy VI's hands. In 162 BC, Ptolemy VI was also involved in a scheme to destabilise the Seleucid kingdom. His agents in Rome helped a Seleucid prince, Demetrius I Soter, escape from captivity and return to Syria to seize control of the Seleucid empire from the under-age king Antiochus V Eupator. Once Demetrius was in power, however, their interests began to diverge and the prospect of war between the two kingdoms returned. In 158 or 154 BC, Ptolemy VI's governor of Cyprus, Archias, attempted to sell the island to Demetrius for 500 talents, but he was caught and hanged himself before this plot came to fruition. In 154 BC, after surviving an assassination attempt which he blamed on his brother, Ptolemy VIII again appealed for assistance against his brother to the Roman Senate which agreed to send a second embassy, led by Gnaeus Cornelius Merula and Lucius Minucius Thermus, equipped with troops, in order to enforce the transfer of Cyprus to his control. In response, Ptolemy VI besieged his younger brother at Lapethus and captured him, with the help of the Cretan League. He persuaded Ptolemy VIII to withdraw from Cyprus, in exchange for continued possession of Cyrenaica, an annual payment of grain, and a promise of marriage to one of his infant daughters (probably Cleopatra Thea) once she came of age.