The Alcântara Valley section of the Águas Livres Aqueduct spans 941 m and features a limestone masonry structure with a central canal gallery covered by a pitched roof and flanked by stone walkways. The aqueduct includes 16 lanterns that provide ventilation and lighting for water quality. Managed by EPAL, the monument also houses the Water Museum. Due to visible material degradation, NCREP was contracted to assess and propose conservation and structural intervention measures for the lanterns. The study was conducted in 4 phases: (1) A high-detail architectural and topographic survey using laser scanning and GPS to create HBIM models; (2) On-site inspections and experimental tests to assess structural properties and conservation; (3) Seismic vulnerability assessment by NCREP and LNEC to identify weaknesses; and (4) Development of intervention measures (not covered in this article). The HBIM models served as a database for mapping anomalies, supporting numerical modelling, and guiding conservation efforts. Inspection results indicated that most alterations affect aesthetics rather than structural stability, though some anomalies, such as metal connectors degradation and global deformations, could impact performance under seismic loads. The seismic analysis involved defining seismic scenarios, developing numerical models of the aqueduct and lanterns, and defining damage thresholds. Findings highlighted vulnerabilities in pinnacles and arch-closing stones, with some lanterns at risk of significant damage or collapse under strong seismic activity. This comprehensive study provided critical insights into the lanterns’ seismic behaviour and helped define necessary structural strengthening measures.