Questions 46-60 are based on the following passage.
The Walls of Rome
Rome, founded on the banks of the Tiber River, boasts two ancient walls that, when they were built, surrounded the city. [A] Although both were built as Q46 walls intended to defend the city protectively and stood ten meters Q47 tall they were erected under different historical circumstances.
Q48 It's though that the Servian Wall was constructed in the early fourth century BCE and named after Servius Tullius, who was the sixth king of Rome. The eleven-kilometer wall encircled Rome's seven hills and stood entirely on the east side of the Tiber River. [B]
The Aurelian Q49 Wall, built in the late third century CE by the Roman Emperor Aurelian, was Q50 more sturdier than the older wall. It was nineteen kilometers long Q51 greatly expanded and surrounded the city of Rome as well as a small section of the Tiber's west bank. Erected almost 600 years after the Servian Wall, the Aurelian Wall protected Rome while the army was away, defending the empire's far-flung frontiers from enemy attacks. [C] The massive wall deterred many enemies who might have been tempted to attack Rome during those intervals the city was sparsely defended.
[D] The Aurelian Wall featured eighteen large gateways permitting both foot and chariot traffic in and out of the city. Q52 In other words, a series of 381 towers and eleven smaller side gates called postems were evenly spaced along the rest of the wall. Q53 Both the postems and the towers served as defensive positions Q54 for protecting Rome. Walkable passages lined the inner side of the wall.
Q55 The Romans used bricks to build the Aurelian Wall.However, only small portions of the Servian Wall Q56 remains, some of which can be seen inside a chain restaurant located beneath Rome's central train station.Q57 It could, perhaps, be considered ironic that remnants of a wall that once protected Q58 the future capital of one of the ancient world's most famous empires are now preserved Q59 and recognized as historically significant by archaeologists.