The rapid urbanization of the 21st century has amplified the demand for sustainable, intelligent, and secure infrastructures. Cyber-Physical Systems (CPS), which integrate computation, communication, and physical processes, have emerged as foundational enablers of smart city ecosystems. When deployed within urban contexts, CPS empower cities to monitor, control, and optimize critical functions such as transportation, energy distribution, water management, and public safety. This paper explores the convergence of CPS and smart cities, focusing on engineering secure, sustainable, and data-driven environments. It highlights the transformative role of real-time sensing, artificial intelligence, and interconnected networks in creating urban ecosystems that are adaptive, efficient, and resilient. Key challenges—including cybersecurity, interoperability, scalability, and ethical governance—are discussed, alongside opportunities for advancing the future of smart city design.