Most of his reign was dominated by co-regents: from 913 until 919 he was under the regency of his mother, while from 920 until 945 he shared the throne with Romanos Lekapenos, whose daughter Helena he married, and his sons. Constantine VII is best known for the "Geoponika" (τά γεοπονικά), an important agronomic treatise compiled during his reign, and his four books, "De Administrando Imperio" (bearing in Greek the heading Πρὸς τὸν ἴδιον υἱὸν Ῥωμανόν), "De Ceremoniis" (Περὶ τῆς Βασιλείου Τάξεως), "De Thematibus" (Περὶ θεμάτων Άνατολῆς καὶ Δύσεως), and "Vita Basilii" (Βίος Βασιλείου).