This paper investigates the seismic actions that affect Qait Bey Fortress in Alexandria- Egypt. It presents the results of scientific studies and examinations to evaluate the deterioration conditions, which affected archaeological buildings in the marine environment. In Alexandria, many monumental sites and stone buildings have suffered from many aggressive factors of deterioration (mechanical, chemical, and biological), which have caused great harmful appearances and threatened to eradicate them. These effects include the chemical actions resulting from seawater and marine aerosol and mechanical actions of water waves. (Qait Bey Fortress), as a case study, was periodically investigated by many scientific techniques through 5 years to check their decay conditions and to define the most suitable conservation approaches and non-destructive methods for preservation. Different techniques and examinations were performed to evaluate the current deterioration state of the fortress. For example, XRD analysis and PM investigation were used to study the mineralogical compositions, lithotype, and petrographic characteristics of the stone samples. SEM was used to investigate the morphological features of the same samples. AAS was also used for studying the chemical constitutes of seawater samples. In addition, microbiological investigations were conducted to evaluate the colored hard crusts that affected the stone surfaces in the fortress. Our results proved that severe deterioration factors highly influenced the fortress by collaborating with chemical, mechanical and biological mechanisms. These mechanisms caused several manifestations, such as abrasion and attrition, crystallizing of salt species, mortar desegregation, pitting and minerals’ honeycomb (Alveolar), color changes, in addition to the accumulation of black and colored biogenic hard crusts.