Complex sentence: Excavation revealed that the pillars, first recorded in 2008, belong to an old church, on account of the presence of a buttress on one of the pillars, characteristic of churches at the time, and evidence of marks on some pillars meant to hold arches.
Split into simpler sentences: Excavation revealed that the pillars, first recorded in 2008, belong to an old church. This was proven on account of the presence of a buttress on one of the pillars, characteristic of churches at the time, and evidence of marks on some pillars meant to hold arches.