In 2004, the Commission for the Preservation of National Monuments declared the "Architectural Complex of Husejnija (Husein-kapetan Gradaščević) Mosque in Gradačac" a national monument of Bosnia and Herzegovina. The mosque belongs to the type of central domed mosque with a portico covered by three small domes. In September/October 2023, cracks were observed on six arches, the capitals of two columns, and the base of one column in the portico of the mosque. Geotechnical investigative works included the creation of three excavations and two boreholes with continuous Standard Penetration Tests (SPT). The excavations reveal layers below the ground level, consisting of a well-bound sandy artificial fill from the ground surface to a depth of 1.35 meters, a layer of poorly bound artificial stony material from 1.35 to 2.45 meters, and a layer of natural clay at greater depths. It is assumed that over time, due to water seepage from the hillside and rainfall runoff from the mosque, there has been a change in the physical-mechanical properties of the foundation soil and partial settling of the portico structure. In addition to the existing channel on two sides of the mosque, a drainage ring around the building and a drainage curtain on the uphill slope have been designed. Also, underpinning of the portico foundations in alternating segments has been designed to strengthen the stone masonry layer and prevent further settling and development of cracks in the portico elements. After the works are completed, a 12-month monitoring period is planned, followed by an analysis and repair of the cracks.

Minarets, tall structures, connected or not to the mosque attract attention due to their specific architectural features. Vulnerability to seismic damage has been witnessed throughout history on tall and slender structures after earthquake ground motions. In that respect, it is of the utmost importance to investigate the dynamic characteristics and resilience of historical stone minarets. This paper aims to provide the results of an on-site dynamic investigation of a stone minaret in Mostar and deliver its seismic assessment. The minaret is part of the Tabačica mosque built at the turn of the 16th and 17th century in the City of Mostar, Bosnia and Herzegovina. The on-site investigation comprised dynamic identification of the minaret by ambient vibration testing and qualitative estimation of the masonry wall by sonic pulse velocity testing. Besides the modal analysis a time-history analysis was performed by using the Applied Element Method (AEM), considered an appropriate tool for assessing the behavior of historic masonry structures. A good match is found between the first natural frequency obtained by the on-site investigation and the modal analysis which is a solid basis for further seismic assessment of the minaret as a slender tower-like structure. The concentration of stresses is observed at the transition zones.