This is a question that arose for me a few years ago when reading the Engels book on the logistics of Alexander's army, but I ended up forgetting about it because it was grad school and I had other shit to do.
Basically my question is this:
Given that a sarissa is about six meters and extremely unwieldy to just be carrying around all the time when you and several thousand of your best friends are walking from Pella to India and back, including down the godforsaken Makran coast, you probably don't want to have it in your hands all the damn time.
But you still want to have it when you need to kill pesky foreigners who don't realize yet that their land now is your land.
So, you could pack a bunch of them onto horses, but they still are probably a little too big for that. Wagons might work but the ancient Greek words Arrian used for the animals in the baggage train indicate the army didn't have wagons. It might work to split the shafts down the middle for travel, and maybe screw them back together when it's time to kill people, but we'd have found like a bajillion little metal pieces that screw together, and somebody would probably have mentioned it, right?
How did they get thousands of eighteen-foot long spears from one place to another? Did individual soldiers seriously just carry them all damn day?
It might work to split the shafts down the middle for travel, and maybe screw them back together when it's time to kill people, but we'd have found like a bajillion little metal pieces that screw together, and somebody would probably have mentioned it, right?
Guess what? You answered your own question. That little thing at the bottom is a coupling sleeve that joins the two halves of the spear shaft. (Apologies for the terrible image quality. Artist's impression here.)
If an army was suddenly attacked, the sarissa was not an ideal weapon; for effective use, there had to be room and time for the pike phalanx to get into formation. This is why Greek and Macedonian armies relied on a screen of light infantry and cavalry when on the march. The Macedonians also employed thousands of more flexible Greek hoplite mercenaries and the elite corps of hypaspists ("shieldbearers") in case there was hand-to-hand fighting to be done. So in a well-managed army there was no need for the sarissa to be always ready for action.
