Training dwarves to use a crossbow takes a fairly long time if shooting on the range. And an awful lot of practice bolts too. I recently started a new map, to the cry of "You have located Arak Arosh, "The Shafts of Dimming", a cave."
This was then followed by a spam of "X cancels job, interrupted by bronze colossus." Disregarding the problems with embarking onto a colossus' lap, this was an opportunity to try something I have had in mind.
This fellow, a local resident, obviously not too impressed by his new neighbours, proceeded to chase and kill my guys around the map for a while. Luckily, I managed to build up a wall around four of the dwarves and the food I had brought, and I settled down underground to plan my revenge.
code:
my base
+++..++++++
+++..++++++
+++..++++++
+++==++++++
+++==++++++
+++DD++++++++++++++++++
+++..........===......
+++..........===...... -> outside
+++++++++++++++++++++++
Key:
. - floor
= - bridge
+ - wall
D - door
So, what we have here - two pits along a corridor with a few tiles inbetween, the pits bridged (retracting) with a lever attached to both, doors between the pits, then a corridor dug to outside from the other end. Then, with the aid of a handy migrant group I lured the colossus into the corridor. I locked the doors just before he reached them, and while he was bashing away at them, I retracted the bridges. Hey presto, my own pet colossus!
But why not just trap the guy in a regular cage, say? For a few simple reasons. a) you get a lot more experience as a marksdwarf for shooting living creatures.
b) colossus heal very quickly
c) arrows do most of their damage by piercing critical organs, which colossus have none of.
You do the math.
Recruit to Elite within a season, tops