Which retail innovation did ancient Romans introduce that is considered the world's first shopping mall concept?

Before modern shopping malls and e-commerce platforms, ancient civilizations had their own innovative retail systems. From the agoras of Greece to the marketplaces of Mesopotamia, these civilizations developed sophisticated commercial networks that influenced retail concepts we still use today. This trivia question explores how ancient Romans revolutionized the shopping experience with an architectural innovation that shaped retail spaces for centuries to come.

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Trajan's Market, a multi-level complex with over 150 shops and offices
The Forum Venalium, a subscription-based marketplace where merchants paid monthly fees for permanent stalls
The Mercatus Maximus, featuring the first documented use of branded shop signage and product guarantees
The Emporium Romanum, which introduced the first customer loyalty program using clay tokens