The subject matter of monumental Byzantine art was primarily religious and imperial: the two themes are often combined, as in the portraits of later Byzantine emperors that decorated the interior of the sixth-century church of Hagia Sophia in Constantinople. These preoccupations are partly a result of the pious and autocratic nature of Byzantine society, and partly a result of its economic structure: the wealth of the empire was concentrated in the hands of the church and the imperial office, which had the greatest opportunity to undertake monumental artistic commissions.