Passage: After his victory in the civil war, Muawiyah launched a series of attacks against Byzantine holdings in Africa, Sicily and the East. By 670, the Muslim fleet had penetrated into the Sea of Marmara and stayed at Cyzicus during the winter. Four years later, a massive Muslim fleet reappeared in the Marmara and re-established a base at Cyzicus, from there they raided the Byzantine coasts almost at will. Finally in 676, Muawiyah sent an army to invest Constantinople from land as well, beginning the First Arab Siege of the city. Constantine IV (r. 661–685) however used a devastating new weapon that came to be known as "Greek fire", invented by a Christian refugee from Syria named Kallinikos of Heliopolis, to decisively defeat the attacking Umayyad navy in the Sea of Marmara, resulting in the lifting of the siege in 678. The returning Muslim fleet suffered further losses due to storms, while the army lost many men to the thematic armies who attacked them on their route back.Among those killed in the siege was Eyup, the standard bearer of Muhammed and the last of his companions; to Muslims today, his tomb is considered one of the holiest sites in Istanbul. The Byzantine victory over the invading Umayyads halted the Islamic expansion into Europe for almost thirty years.

Question: When did Muawiyah send his army?
676