After the Al Muaiam assassination, you return to Animus and overhear a conversation about how they are going to kill you. Use Eagle Vision and you'll see some letters on the floor.

M O R Y M N O E S
E N C E O L C H T
H O N B T L O T C
T D E O S A T O A
P E D S N L S T F
L D D U O O E T E
E A I E I R I N T
H S H K T T K E R
T U A A A N S S A

Decode these by reading from the bottom right to the top right. After decoding, it spells out:

ARTEFACTS SENT TO THE SKIES TO CONTROL ALL NATIONS TO MAKE US OBEY A HIDDEN CRUSADE DO NOT HELP THEM

Do the same on the other side of the Amnius to reveal:

A
D R H
O O D T M
W H B I T D O
E U S Y S I N S E
A R O O M R E A Y N R
I S E Y T N I D L M I D E
T W I H W Y I E A U D A Y H T

Which spells out:

THEY DRAINED MY SOUL AND MADE IT THEIRS I DRAINED MY BODY TO SHOW YOU WHERE I SAW IT