This is a single shoulder strap for an enlisted man/NCO from Magdeburgisches Pionier-Bataillon Nr 4. Pioniere were the Imperial German Army’s engineers, responsible for building bridges, roads, etc. The unit was founded in 1816, the year after the Napoleonic Wars’ conclusion. The Bataillon was garrisoned at Magdeburg and attached to the Prussian IV. Armeekorps.
The shoulder strap measures 2″ x 5 ½.” Its obverse is black with red trim around its edges, and a red embroidered “4” in its center. Some slight evidence of moth tracking is evident on its obverse. Its reverse is covered with feldgrau felt.