The mosque's construction was not a solo act of royal piety. Three sources of wealth converged to make it possible. The Sultanate of Deli provided the royal mandate and prestige. The Deli Maatschappij -- the Dutch plantation company that had grown enormously wealthy from tobacco cultivation on Sumatra's east coast -- contributed funding, reflecting the entanglement of colonial commerce and local power. And Tjong A Fie, the wealthiest businessman in Medan at the time, a Chinese-Indonesian merchant who had built a fortune in trading and real estate, provided additional financing. The collaboration was itself remarkable: a Malay sultan, a Dutch corporation, and a Chinese magnate jointly funding an Islamic house of worship. That alliance of interests -- cultural, commercial, and communal -- produced a building that reflected all of its patrons without belonging exclusively to any of them.

The mosque was originally designed by the Dutch architect Theodoor van Erp, the same man who had designed the Maimoon Palace. But before construction progressed far, the Dutch colonial government summoned van Erp to Central Java for a project of a different scale entirely: the restoration of Borobudur, the ninth-century Buddhist temple that remains one of the largest religious monuments in the world. The mosque was handed to architect J.A. Tingdeman, who inherited van Erp's octagonal concept and developed it into something distinctive. Tingdeman combined elements from Morocco, Europe, and the Middle East into a symmetrical layout built on an eight-sided floor plan. The result was an inner chamber unlike most conventional mosques -- not the typical rectangular prayer hall, but a space defined by its geometry, with eight main pillars supporting the central dome and four aisles radiating outward on all sides.

Walk through the mosque and the building materials tell a story of global trade routes converging on colonial Sumatra. The marble came from Italy, Germany, and China. The stained glass in the chandeliers was imported from France, its designs bridging Art Nouveau -- the European decorative movement that flourished from 1890 to 1914 -- and Islamic geometric art. The mihrab, the niche indicating the direction of Mecca, is carved from marble and topped with a pointed dome. Walls, ceilings, pillars, and arches are layered with floral and botanical ornamentation. The arched windows and porches recall the Islamic kingdoms of medieval Spain, while the main dome follows Turkish models. Five domes crown the structure: the large central dome and four smaller ones atop the corner porches. The minaret blends Egyptian, Iranian, and Arabian influences into a single ornate tower. No single tradition dominates. Instead, the mosque reads as a catalog of Islamic architectural achievement assembled under one extraordinary roof.

The octagonal plan sets Al-Mashun apart from nearly every other mosque in Indonesia. Most mosques follow rectangular or square floor plans oriented toward Mecca. Tingdeman's design breaks that convention with an eight-sided symmetry that produces a series of spatial surprises as you move through the building. Four wings extend to the south, east, north, and west, each with its own high-vaulted black roof porch. The main prayer room occupies the center, surrounded by the four aisles with their rows of arched windows. Smaller porches protrude outward, adding irregularity to what could have been rigid geometry. The windows are wooden-framed with precious stained glass, and the play of colored light across the ornamented interior surfaces changes throughout the day. The dome shape echoes the Grand Mosque of Banda Aceh, connecting Al-Mashun to a broader Acehnese and Sumatran architectural tradition even as its form departs from regional norms.