Legendary king of early Ireland, cited at the beginning of chronicle history and thought to have lived c. ad 300. He ruled for a seven-year term as part of a twenty-one-year cycle with his kinsmen (sometimes brothers, sometimes cousins) Áed Ruad and Díthorba. Seven magicians, seven poets, and seven lords of Ulster saw to it that this agreement was kept. When Áed Ruad died, his daughter Macha (2) was elected to rule. Cimbáeth and Díthorba opposed her at first, but Cimbáeth later made peace and married her, while she killed Díthorba. Macha (2) dominated Cimbáeth, and obliged him to build the royal fort of Emain Macha.