Browning probably chose to set this poem in an historical period as it was normal for the woman to be regarded as a possession of the man and have no real rights. In this poem the idea is taken to extremes as the Duke kills her because he feels she has been disloyal and he appears to face no punishment for this. Browning was probably interested in the changing nature of women's place in society as during the Victorian period there were debates about women's property rights, divorce etc. This led eventually to the sufferage movement and the gaining of the vote for women.
Therefore this historical period was a complete patriarchy and Browning no doubt found it interesting to consider what it would have been like to live in that time.