Simplify the following text for a Grade 7 native English-speaking person.
Original: In Middle Ages , when the order of the liturgical feasts was partly determined by the date of Easter , the custom was early established in the Western Church of drawing up tables to indicate that date for a certain number of years or even centuries .
Simplified: In the Middle Ages in the Western Church there were written tables to show that date of Easter for a certain number of years or even centuries .