Simplify the following text for a Grade 9 native English-speaking person.
Original: Constantine had invited all 1800 bishops of the Christian church ( about 1000 in the east and 800 in the west ) , but only 250 to 320 bishops actually participated .
Simplified: Constantine had invited all 1800 bishops of the Christian church ( about 1000 in the east and 800 in the west ) , but a smaller and unknown number attended .