common. The handscroll was the one of the main formats for texts up until the Tang dynasty (618–907). Since the Three Kingdoms (220–280), the handscroll became a standard form for mounting artwork. New styles were developed over time. Hanging scroll: Hanging scrolls originated in their earliest form from literature and other texts written on bamboo strips and silk banners in ancient China. The earliest hanging scrolls are related to and developed from silk banners in early Chinese history. These banners were long and hung vertically on walls. Such silk banners and hanging scroll paintings were found at Mawangdui dating back to the Han Dynasty (206 BCE – 220 CE). By the time of the Tang Dynasty (618–907), the aesthetic and structural objectives for hanging scrolls were summarized, which are still followed to this day. During the early Song Dynasty (960–1279), the scrolls became well suited to the art styles of the artists, consequently hanging scrolls were made in many different sizes and proportions. Heavy moldboard iron plow: Although use of the simple wooden ard in China must have preceded it, the earliest discovered Chinese iron plows date to roughly 500 BC, during the Zhou Dynasty (1122–256 BC) and were flat, V-shaped, and mounted on wooden poles and handles. By the 3rd century BC, improved iron casting techniques led to the development of the heavy moldboard plow, seen in Han Dynasty (202 BC – 220 AD) artwork such as tomb carved bricks. The moldboard allowed the Chinese to turn farm soil without clogging the plowshare with dirt, which was flung off the wheelbarrow via slanted wings on both sides. While the frame of excavated plowshares dating to the Warring States period (403–221 BC) were made mostly of perishable wood except for the iron blade, the frame of excavated plowshares dating to the Han Dynasty were made entirely of solid iron with the moldboard attached to the top to turn the soil. Helicopter rotor and bamboo-copter: The use of a helicopter rotor for vertical flight has existed since 400 BC in the form of the bamboo-copter, an ancient Chinese toy. The bamboo-copter is spun by rolling a stick attached to a rotor. The spinning creates lift, and the toy flies when released. The Jin dynasty philosopher and politician Ge Hong's book the Baopuzi (Master Who Embraces Simplicity), written around 317, describes the apocryphal use of a possible rotor in aircraft: "Some have