[Illustration: PLATE VIII.--16th Century Knocker, Lion type, Striker of first type; Georgian Urn type, in use on modern house; Mexican Knocker of the Hammer type; Hammer type Knocker, 18th Century, Charles P. Waters House.] Old door knockers vary as to size according to the date of their construction. Many are of odd design, having been made to fit doors of unusual shapes, and the ornamentation is as varied as the shapes. The most elaborate knockers depict such ideas as Medusa's head, Garlands of Roses, and, in many cases, animals' heads, while the simple ones show oval or plain shapes, with border decorated with bead or fretwork. [Illustration: PLATE IX.--Eagle Knocker; Eagle Knocker, Rogers House, Danvers, Mass.; Medusa head, elaborate early type; Garland type of Knocker.] The shape of the knocker is of great assistance in classification, as is the metal used. The most common type has the striker round or stirrup-shaped. This is either plain or ornamented with twisted forms, with wreathing or masks, and the plate is formed of a rosette or lion's head. In the second type, the striker is hammer-shaped, the handle often showing a split and straplike formation, while the plate and knob are plain. This is an early type, as is shown from the fact that specimens still exist that are not unlike Byzantine and Saracenic forms. It is to this type that the exquisite iron-chiseled knockers of Henry II and Louis XIV belong. The lyre or elongated loop drawn down to form the striker constitute the third style. Masks, snakes, dragons, and human figures belong to this class, and, on account of the elaborate workmanship employed, these are often found in brass and bronze. This type shows ornamentation lavished on the striker, while the plate is very plain. The greatest difference noted in all these classes is that in the third type the escutcheon or plate by which the knocker is fastened to the door is of little importance, while in the first two types it is the leading motive. During the Gothic period, the design was diamond-shape, richly decorated with pierced work, and while this same motif was retained in the making of the Renaissance knocker, it was frequently varied by the double-headed or some similar style.