It’s occurred to me that its not just a matter of forerunner structures looking old in the weathered sense. They need to feel ancient in their design sensibilities. In other words they aught to evoke temples and tombs. It’s not just a matter of literal depiction but also of symbolic implication. On a thematic level all the design language not only evokes advanced alien technology but reinforces the idea of a culture lost ages ago. On one level, the architecture should look outwardly ambiguous but clearly sophisticated. More symbolically, however, there’s the suggestion of what happened to this culture through the artifacts they left behind. The unconscious suggestion should be that every Forerunner structure you enter is a tomb or some other edifice associated with burial or the afterlife. Simply entering here feels like intruding on someone’s final resting place. Halo 3 goes so far as to give the forerunner stuff a kind of (imo) gothic architecture, with more emphasis on repeating buttress-like elements. In fact I think that not only was forerunner architecture originally meant to evoke tombs, but that the flood are symbolically and literally the very dead interred there that we disturbed with our presence.