Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.

• The regularity and power of stone walls inspired Romans attempting to unify the parts of their realm.
• Although the Romans used different types of designs when building their walls, they used regular controls to maintain their realm.
• Several types of control united the Roman realm, just as design and cement held Roman walls together.
• Romans built walls to unite the various parts of their realm into a single entity, which was controlled by powerful laws.

This is a multiple choice.