Complex sentence: The highest status toga, the solidly purple, gold-embroidered "toga picta" could be worn only at particular ceremonies by the highest ranking magistrates, whose privilege and prestige were protected, at least in principle, by tradition, custom and sumptuary laws.
Split into simpler sentences: The highest status toga, the solidly purple, gold-embroidered "toga picta" could be worn only at particular ceremonies by the highest ranking magistrates. Aristocratic privilege and prestige were protected by tradition, custom and sumptuary laws.