These are the Seljuk tombstones in Ahlat, Bitlis left by the Ahlatshah dynasty dating back to the 12th century. Not a single Turkish article would mention this but Ahlat (Khlat in Armenian) is actually an ancient Armenian town and I think these Seljuk tombstones clearly have an Armenian influence, in fact there ‘was’ an Armenian cemetery and many khachkars (Armenian cross-stones) in Ahlat. I believe it’s even possible that these were made by Armenian craftsmen since you don’t see Muslim tombstones like these anywhere else in Turkey and just look at the intricate stonework.
‘Though the history of the Ahlat dates back to 900 BC, its famous for her tombstones dating to 12th-15th centuries. It has an important place in the Islamic world in their variation within Anatolian tomb architecture in dimension and design. Tombstones in the vast Ahlat Seljuq graveyard are some of the most outstanding tombstones of the Seljuq (early Turkish) period in Anatolia. Tombstones, covered in lichen and leaning at drunken angles, many are 2 m tall, carved with elaborated designs showing Armenian influence (floral and geometric motiffs). The inscriptions (in Arabic and Persian) on the tombstones are generally in verse, extolling symbolic virtues.’ (x)