This steelyard weight was discovered at Montgomery Castle in the spring of 1970. It has been identified as an armorial steelyard weight which carries the arms of England, Poitou, Richard, Earl of Cornwall, and the Holy Roman Empire. It is believed to date from the second half of the thirteenth century. The shield shown here is that of a double-headed eagle representing the Hansa merchants.

Building work on Montgomery Castle was commenced by Henry III in 1233 on the site of an old 'motte and bailey' castle. The new castle was built during Henry III's campaign against Llywelyn ap Iorwerth (Llywelyn the Great) and was given to Hubert de Burgh in 1228. It was held by the Mortimers in the 14th century. During the English Civil War, Montgomery became the site of a large battle in September 1644, with anything up to 9,000 troops involved. The castle surrendered to the Parliamentarians and was demolished after the war on the order of Parliament.

Sources:
http://www.castlewales.com/montgom.html
Cadw, 'A Nation Under Siege: The Civil War in Wales, 1642-48' (London, HMSO, 1991).