The SHRINE of IMAMZADEH Sahl ibn Ali (peace be upon him) stands as a prominent architectural and religious monument in the town of Astaneh, located 40 kilometers southwest of Arak, in the Markazi province of Iran, nestled in the eastern foothills of the Zagros mountain range. The structure is recognised as one of the most significant surviving examples of the four-iwan architectural style in religious architecture across Iran. Based on historical documents and early stone carvings, the initial construction of the SHRINE is believed to date back to the 4th century AH (10th century CE), during the reign of the Buyid dynasty. A carved inscription dated 772 AH on the wooden sarcophagus inside the SHRINE confirms the site's longstanding sacred and religious significance, mentioning Sahl ibn Ali, the son of Imam Ali (peace be upon him).The current architectural form of the SHRINE primarily dates back to the Safavid era, with major renovations and additions carried out during the Qajar and Pahlavi periods. The layout includes a central courtyard with four iwans, a main domed chamber featuring a double-shell structure and an octagonal plan, a surrounding ambulatory, and additional spaces such as a smaller eastern dome chamber, prayer halls, and side chambers. Over time, several historical structures including a religious school, a caravanserai, and a traditional hammam were lost due to neglect and destruction. Today, only the fourth courtyard remains in use, serving as the main access point for pilgrims. An inscription dated 1150 AH located above the entrance of the sacred sanctuary, or Rawda-ye Monavvareh, attributes the Safavid-era restoration to the renowned architect Ali Akbar Isfahani. Further historical evidence, including references in the Habib al-Siyar chronicles, records the visit of Shah ISMAIL I to the SHRINE, indicating its prominence prior to Safavid patronage. Mohammad Hassan Khan Etemad al-Saltaneh also discusses the etymology of the name Astaneh, linking it to the burial site of Sahl ibn Ali. A deed of endowment (waqf-nama) dated 842 AH further confirms that the site held religious significance even before Shah ISMAIL's restoration, reinforcing the continuity of sacred function throughout centuries The northern and southern iwans, along with the main domed chamber, host the majority of the SHRINE's architectural ornamentation. These decorative features, in addition to their structural and aesthetic functions, reflect deep Shiite religious symbolism, contributing to the SHRINE’s lasting spiritual significance among rulers and local populations throughout Iranian history. A semiotic analysis of the ornamental motifs reveals strong ties to Shiite mysticism and metaphysical thought. Sunburst (shamsa) designs symbolise divine unity and centrality; geometric motifs such as squares, stars, and hexagons represent cosmic balance, guidance, and perfection, respectively. Plant-based motifs—grape leaves, cypress trees, tulips, poppies—and birds like peacocks, nightingales, and doves symbolise paradise, resurrection, and purity.The SHRINE incorporates a rich variety of architectural ornamentation, including Ayeneh-kari, reverse-glass painting, polychrome tilework (haft-rang), Kufic and Bannai inscriptions, Moqarnas vaulting, and woodwork crafts such as girih tiling, carved wooden doors, and Qavareh-bori. The calligraphy is executed in Thuluth and Nastaliq scripts through painting on plaster, carved stucco techniques (Koshteh-bori), and stone engraving. These decorative elements carry floral, geometric, and figurative motifs, with Ayeneh-kari (mirror work), inscriptions, and wall painting forming the dominant visual features. The western iwan, enclosed with a triple sash door (Se-dari) and known as the Rawda-ye Monavvareh, is the most elaborately adorned space within the complex. The mirror mosaics here cover the ceilings and walls with complex light-reflecting compositions, executed during the Pahlavi era (circa 1342 SH), bearing the signature of Haj Ebrahim Talaei. Additional mirror work by the Alaei brothers in the subsequent decade, while crafted with notable precision, lacks stylistic harmony with the older Safavid context, resulting in partial degradation due to moisture and oxidation. The wooden elements, such as the carved doors, wooden boxes, and old latticework, although their dates are not always documented, mostly belong to the Qajar period. The tilework features a palette of creamy yellow and blue tones, adorned with arabesques, floral Shah Abbasi motifs, Kufic inscriptions, and Bannai geometric tilework. These tiles embellish the courtyard façades, the iwans, window spandrels, and the dome base. Although parts of the dome were once tiled, these decorations have largely deterioratedThe murals, stylistically belonging to the late Qajar period based on restoration records and the aesthetic nature of the floral and avian motifs, demonstrate varied techniques and qualities, likely executed by different artists over time. These wall paintings exhibit a blend of realism and symbolic abstraction, portraying paradise-inspired scenes through vivid colours and layered compositions. Limited but significant examples of reverse-glass painting accompany mirror works. Among these are religious portraits (shamayel), including depictions of Imam Ali (a.s.) with his sons, executed with radiant halos and emotional expressiveness, as well as portrayals of clerics, all framed within decorative wooden borders. According to inscriptions within the SHRINE, these artworks are attributed to artists such as Master Ali Baba-ye Naqqash-Bashi and Mashhadi Ebrahim, the mirror artisan.The stucco stalactites (muqarnas) serve both decorative and structural purposes, seen prominently in the entrance of the Rawda-ye Monavvareh and under the dome’s transitional zones. These vaults are arranged in symmetrical, geometric patterns and painted to amplify their visual rhythm and hierarchy. The dome’s central sunburst creates a focal point that guides the viewer’s eye downward across the entirety of the ornamental scheme, connecting the spiritual symbolism of the celestial with the earthly space of the worshipper.One of the most important features of this SHRINE is the extensive use of calligraphy, ranging from Qur'anic verses in Thuluth script to Persian poetic verses and waqf (endowment) inscriptions in Nastaliq. These inscriptions were applied using a combination of techniques: carved stone, painted plaster, and Koshteh-bori (a technique where raised relief text is shaped on plaster). The iconographic and symbolic meanings of these texts—particularly those praising God, the Prophet, and Imams—underscore the religious reverence embedded in the architecture.This study adopts a qualitative, descriptive-analytical methodology and combines historical-documentary research with field observations. In addition to archival studies and literature review, site visits and photographic documentation were conducted. Interviews with local caretakers and historians enriched the empirical understanding of the SHRINE’s transformations. Each decorative element was documented, categorized, and compared against stylistic typologies from Safavid, Qajar, and early Pahlavi periods.The findings reveal that while the SHRINE preserves exceptional artistic and historical value, many of its original elements have deteriorated over time due to humidity, inappropriate restorations, and lack of conservation plans. Mirror surfaces have oxidised, tiles have faded or chipped, and some wooden elements were replaced without stylistic compatibility. The study emphasises the need for a comprehensive and scholarly-based restoration program, prioritising authenticity and cultural continuity. Furthermore, this typological classification of motifs contributes to broader discourses on Iranian-Islamic ornamentation, especially in the context of religious architecture, offering insights into both the aesthetic evolution and the spiritual expressions of Shiite culture in Iran.In conclusion, the IMAMZADEH Sahl ibn Ali SHRINE stands as a remarkable embodiment of religious art and architecture in Iran, encapsulating centuries of devotional creativity and craftsmanship. Through a systematic analysis of its decorative arts, the study contributes to the documentation, preservation, and appreciation of Iran's sacred architectural heritageBeyond its ornamental richness, the SHRINE reflects a layered narrative of regional history, artistic patronage, and collective religious memory. It bears witness to a continuum of aesthetic choices shaped by dynastic ideologies, theological symbolism, and local craftsmanship. The presence of inscriptions from various historical phases, as well as the diversity of techniques—from Ayeneh-kari (mirror mosaics) to glazed ceramics and hand-carved woodwork—exemplifies the adaptability of Iranian religious architecture across centuries. Each layer, whether original or restored, reveals specific cultural priorities and evolving expressions of faith.Furthermore, the integration of symbolic elements within architectural features—such as the metaphoric use of birds for spiritual ascent, or geometric repetition to evoke divine infinity—transforms the SHRINE into a visual theology. It is not merely a burial structure but a sacred space where form and ornament converge to narrate transcendental truths. The syncretic harmony between space, material, light, and text in this SHRINE resonates deeply with the broader canon of Islamic art and architecture, positioning it as a valuable site for future interdisciplinary scholarship.