This is a well known thread from October 2010 (well, the first 12 posts are from then):
https://bitcointalksearch.org/topic/patch-increase-block-size-limit-1347Jeff Garzik proposed a patch to lift the max block size limit. It can be seen from the code that the size limit at that time was already 1MB.
We should be able to at least match Paypal's average transaction rate...
diff --git a/main.h b/main.h
...
-static const unsigned int MAX_BLOCK_SIZE = 1000000;
...
...
Theymos and Satoshi warned against the patch:
Applying this patch will make you incompatible with other Bitcoin clients.
+1 theymos. Don't use this patch, it'll make you incompatible with the network, to your own detriment.
We can phase in a change later if we get closer to needing it.
This is the thread in which Satoshi had an often quoted reply about how to raise the limit:
It can be phased in, like:
if (blocknumber > 115000)
maxblocksize = largerlimit
It can start being in versions way ahead, so by the time it reaches that block number and goes into effect, the older versions that don't have it are already obsolete.
When we're near the cutoff block number, I can put an alert to old versions to make sure they know they have to upgrade.
I wasn't around back then, but it seems clear to me that Satoshi was still around when the 1MB limit was put in place. I know I've read that he introduced it himself in mid-2010, but I don't have a source to back that up. Is there some evidence that the limit was originally smaller than 1MB and then was lifted (twice?) until it was 1MB? I have to admit, I'm skeptical of the claim that it's been raised before. But I could be wrong.