«The symbolism of the keys is brought out in an ingenious and interpretative fashion by heraldic art. One of the keys is of or, the other of argent. The golden key, which points upwards on the dexter side, signifies the power that extends even to Heaven. The silver key, which must point up to the sinister side, symbolizes the power over all the faithful on earth. The two are often linked by a cordon gules as a sign of the union of the two powers. The handles are turned downwards, for they are in the hand of the Pope, Christ's lieutenant on earth. The wards point upwards, for the power of binding and loosing engages Heaven itself»
