Okay, this is my first FAQ/guide/list that I've done in years that wasn't a collaborative effort, so all feedback is welcome.

I did the best I could in describing where/how to get these, if you feel it is unclear or have a better way to describe it, please let me know. This list was made by me and only this site (
www.xbox360achievements.org) and
www.gamefaqs.com have my permission to use it. On to the list:
Pigeons
1 - Right next to the Olympic official who asks you to free 10 pigeons.
2 & 3 - In an alcove, down a path to the left, past Pigeon #1.
4 - 6 - In and around a "tent" at the end of the path.
7 - 10 - At the top of the 1st wall you climb.
11 & 12 - Just to the right when you enter the Olympic village.
13 & 14 - Behind the area where Lovestorix is working on his chariot.
15 & 16 - In a small room by Shield #3
17 - 19 - At the top of the hill with the basket balls rolling down it.
20 & 21 - On the first level of the wooden platform by the second Romanophone.
22 - In Doctormabus' hideout, near the first wall that you climb.
23 - Next to the switch to lower the green box in Doctormabus' lair.
24 & 25 - Below the room with the third Romanophone in Doctormabus' lair.
26 - 28 - From the elevated walkway for Shield #5, push the block to the ground. Then use this block to climb the platforms to these Pigeons. Alternately, you can use the 'jump dash' attack from the ledge at the top of the hill (near the toadball machine) to reach these Pigeons.
29 & 30 - In the VIP area, near the closed door at the far end. Turn right and jump up on a grassy hill.
31 & 32 - At the top of the building whose opened up by Romanophone #4. Climb on the wall at the top to reach them.
33 & 34 - Outside Brutus' quarters, put a small block on the switch and then send Romans through the target to open the gate underneath it.
35 - 37 - From the first cable car end point, jump across to an area that has these pigeons.
38 - After flipping the switch at the top of the first climbing wall in the Underground, go back to the bottom of it and this is in an alcove to the right.
39 - On Obelix's path, between his first switch and where he meets up with Asterix again in the Underground.
40 - Shortly after Pigeon #39, behind a "step" platform.
41 - Near the second climbing wall in the Underground (this wall is actually on Obelix's path, but Asterix has to go this way to work a mechanism before Obelix can come this way).
42 & 43 - Use Obelix to pull Asterix in the cable car the VIP zone. At the end of the cable car ride where the switch is to open the door to the chariot race, use the wall climbing spots to drop under that area to get these two pigeons.
44 & 45 - Have Asterix retrace Obelix's steps to get Pigeons 42 & 43. On the second set of buildings you hop on, look for climbing walls. Follow these to get these pigeons.
46 - 48 - Return to the City where you had to drop Romans from the clouds and climb the wall by the right switch. Make your way around to a switch and stand on it. Switch to Obelix and have him jump on the column that is going up and down. At the top of the column, have him jump and walk around on the other columns to get these pigeons.
49 - 50 - From the switch for the previous pigeons, drop down to get these pigeons.
For the last two sets of pigeons, I couldn't get these until after I beat the game, as I couldn't get onto the building with the switch because of the black clouds. I don't know if there is a way around this that I was just missing or not.
Shields
1 - Straight ahead when you enter the Olympic village.
2 - Down the path to the left (the one with all the tents) when you enter the Olympic village.
3 - Go through the door unlocked by jumping on the light-up platform. User the Romanophone to open the gate, then push the block as far as you can. Climb the wall and work you way to the block. Jump to get the shield.
4 - On the second (top) level of the wooden platform by the second Romanophone (above Pigeons 20 & 21).
5 - After chasing Doctormabus on his chariot, head back to his lab. Go through it and exit out onto an elevated walkway. Jump from here to reach this shield at ground level on the rise.
6 - In the City area, after raising the bridge, jump down behind the mechnasim that raised the bridge to reach this shield.
7 - Above Romanophone #4 in the area outside Brutus' quarters.
8 - Found while climbing the first wall in the Underground.
9 - In an alcove on the side of the "waterslide" in the villa (where you are immediately after exiting the Underground).
10 - Jump up on the big block you push to get out of the villa area and then jump on the roof next to that to get this shield.
11 - Move the small block (in the area where all the Romans are after you leave the villa) under the shield floating out of reach in the sky. Jump on the block and then jump to reach the shield.
12 - After you get all 50 pigeons, find the last shild where the statue of Brutus was outside of his chambers.
Magnesia
1 - Near the person who tells you how to climb walls.
2 - On the path up to Doctormabus' lab.
3 - Right there when you fall into the Underground.
Glue
1 - Just past Shield #2 on the path.
2 - Near where the second Romanophone is.
3 - In the City area, send the Greek (training with the boxes on top of him) onto the switch to rotate the target to face outwards. Climb the building with Asterix and send toadballs down to Obelix to kick into the target to lower the gate to the last glue pot.