Sequence 14 - Veni, Vidi, Vici
For a moment you will go back to Desmond, who will immediately decide to know something more about Ezio. Return to the villa - unfortunately to go forward you must have all 30 pages of the Codex. 
Sequence 14 - X Marks The Spot
When you will gather the necessary material go back to the mansion and talk with the group.  Now you have to place thirty pieces of codex on the wall using a special vision .  First, match the edges - they must create a "frame". Then do the rest. The whole should be similar is to a world map.
After a long conversation you need to talk with Mario in his office.  He will send you on a mission to Rome. 
Sequence 14 - In Bocca Al Lupo
Climb on the first beam and jump to the next one.  Use a wooden platform to jump back to the tower. 
Go to the top  and deal with the soldiers. 
Use the lever and go through the gate.  On the other side kill two enemies and climb up using the boxes. Murder the second enemy and activate the second switch. 
Now you have to fight with some enemies and then climb on the tower.  Use a horse to get to the abyss and deal with other soldiers. Now go further. 
Kill the next patrol and climb on the tower (you will find some guards on the top).  Jump to the other side and repeat the same activity with the next tower. 
This time, kill your enemies silently. Hide in a hay  and pull a soldier inside. Run to the second point, and do the same.  Repeat the procedure with the patrol. Climb on the next tower.
At the top, finish your three enemies and then jump down to kill one more guard.  Next you will have to deal with two soldiers and then fight with a large group that will come soon. 
Jump on a building and then on a footbridge.  Then go to the mechanism. 
Get into the room with monks, they will grant you anonymity. We are starting with a group that walks in a circle.  Get close to the guard near the switch. Kill him and use the lever. 
Around the corner the situation will be very similar, except that the monks are standing and guards are walking. Observe their route and then follow the soldier.  Turn left.  Use the switch and quickly enter the church.
In the church use the footbridge to get to the right side.  Use scaffolding and ropes to continue your "journey".
On the last footbridge you will be in a convenient position for the murder.  Unfortunately, it will appear that a surprise is waiting for us. Attack the enemy only when Ezio's clones will be fighting with him. 
After the battle activate two buttons located near the altar to open the passage.  Now go through the corridor. 
Time for a next fight. Your opponent is extremely weak, so just counterattack.  In due time you will be able to finish him by pressing SQUARE.  Go to the chamber and observe what will happen.