Haghia Sophia (built AD537) without doubt is the most majestic building for centuries probably is just surpassed by Taj Mahal. The latter however is just essentially a monument but Haghia is fully functional architecture suitable for congregations. Both of the buildings sourced its building materials from all over the world due to Roman Byzantine and India are both the richest world's empire at their apex times.

Fun facts, most of the mosques all over the world copied the Christian's origin Haghia Sophia's dome based architecture and the dome becomes a generic symbol for mosque in apps, etc. On the other hand, churches all over the world are mainly based on the Gothic architecture. The Gothic architecture is most probably originated from Muslim Spanish empire although it's claimed to have Roman and French influences [1]. This can be seen from the infamous architecture of Great Mosque of Cordoba or Mesquita (built AD784) the world's largest mosque during its time, now a church. The other popular mosque inspired by Mesquita mosque is Spanish Mosque (built AD1906) in Hyderabad, India.

Arguably, the more visually appealing and beautiful architecture based on Haghia Sophia is what made it being adopted by most of the mosques around the world and the demise of Muslim Spanish in the 15th century that really sealed the fate of the Gothic based architecture for adoption in modern mosques.

[1]https://muslimheritage.com/muslim-origin-of-gothic-architect...