Heavy gauge iron bar has hook at one end possibly to attach it into door. Other end has spade-shaped foot to keep door in proper relation to door jam. Middle of bar has a slit through which a loop of some kind would have passed. Iron hook mounted on latch swings over slit and would have kept loop from pulling out. No way to lock the latch and apparently no way to open it from other side so it must have been an internal latch.
L. 39 x W. 4.5 x H. 4 cm (L. 15.4 x. W. 1.8 x H. 1. 6 in)