The Servian Walls are surviving fragments of Rome's early city defences, traditionally linked to King Servius Tullius and largely rebuilt in the early 4th century BC. The most visible stretches show the scale of republican Rome before the imperial city expanded far beyond them.
They are not a single monument with a formal entrance, so treat them as a quick historical stop while moving around Termini, Castro Pretorio, and the Esquilino. The rough tufa blocks are a useful reminder that Rome was already ancient before the Colosseum was built.