Mounted troops had, over the centuries, developed into two different classes. The older type was lightly armed and armored and used largely for scouting and skirmishing. As saddles, armor and weapons became more elaborate, the heavy cavalry developed. In the first few centuries AD, the parthians (Iranians) developed plate armor for mounted warriors and, in effect, invented what we now think of as the "knight." The idea spread west, with the Germans and East Romans (whose capital was Constantinople) being first to adopt this new style of fighting. The stirrup came into use at the same time, as did the idea of using a heavy lance. By the sixth century, the system was complete and the knight remained a common feature of warfare for the next thousand years.