This is Orberg's LLPSI Cap XLII - describing Romulus' disappearance before the assembly
Romani iuvenes, postquam ex tam turbido die serena et tranquilla lux rediit, ubi vacuam sedem regiam viderunt, velut si orbi facti essent, maesti aliquamdiu siluerunt.
I'm slightly (perhaps very) confused about the tense and mood of velut si orbi facti essent.
facti essent is pluperfect subjunctive... so my whole translation of the sentence is..
The Roman youth when after such an eventful day a peaceful and calm light had returned, seeing the empty throne, almost making a circle [i.e. standing in a circle around the empty throne], were silent for some time.