The macroscopic level of software design is software architecture, and architecture choices impact system qualities, including sustainability. Several studies have explored means to achieve sustainable architectures: those can endure over the long-term. However, there needs to be a broader understanding of such architectures. The contribution of this paper is to offer a view of the characteristics of sustainable software architectures. We first scrutinized the scientific literature and systematically selected 82 studies. We extracted 51 characteristics from non-domain-specific studies and 37 from domain-specific ones, categorized into themes, and then analyzed the papers on those categories. We conclude that no new technical approaches have been proposed for sustainable architectures; the only newness is a change in the mindset, towards greater awareness of sustainability. We also found that the dimensions of sustainability—technical, social, economic, and environmental—have yet to be properly addressed.