This is a pair of Portuguese Estribos de Caixa - Box or Body Stirrups.
Each of these stirrups is constructed in wood, there are many old woodworm holes, but the wood has been treated & the woodworm is long dead.
The fronts are covered with a sheet of brass and decorated with a crest with a crown - presumably linked to a royal household
Each stirrup has a brass band around its centre which holds a suspension loop.
Dimensions : Width 5¾" (14.5cm), height 5¾" (14.5cm), length 9¼" (23.5cm)
Weight : 2.2kg (4lb 13oz)
Ref : stirrup235