Under emperor Claudius, Rome landed an army in Britain and conquered it. Roman Britain remained Roman for the next 400 years-untill the general commanding the two army legions took them back to Rome (he needed them in his quest to become emperor). During these 400 years, how easy (or hard) would it have been to send soldiers across the Irish Sea and conquer Ireland? Ireland had gold and other stuff the Romans wanted-why didn’t they extend their empire to that island?
There wasn’t much there to rule. Later England joined it up because having a neighbour as a backdoor was a threat — had there been no British Isles one of the other sea-neighbours would have done the same, if only to deny it to another [ people have no real idea of the dislike between France and Spain in the past ] — not for wealth: Ireland was no threat to the Roman Empire.
The Romans went where the money was: they weren’t into imperialism for anyone else’s good. And since the imperial system took over Augustus had laid limits to expansion: it was under the senate of the previous few centuries Rome had aggressively grabbed most of her provinces.
And a little later they were mainly fighting on the defensive.
If they’d wanted it they could have conquered it, but at the expense of drawing resources from somewhere else. It wasn’t a priority and there were better, more lucrative territories to focus on.
I would think that England was the end of their logistical abilities to conquer and administer an new land.
Could they have conquered Ireland, I suspect so. Would they be able to hold on for 400 years, I suspect not.
Indeed. Less than a century after Claudius’s invasion, Hadrian had set a limit on the empire’s expansion - hence Hadrian’s Wall. Rome had enough to keep them busy, both in terms of defence and economic opportunities, at other extremities of the empire.
Anachronism nitpick: the Romans were never in England, only in what is now England. At the time, lacking English people, that chunk of the island of Britain didn’t have a distinct name.
Well, by the same token they couldn’t have conquered Ireland, either, since the locals mostly called it Ériu and the Romans called it Hibernia.
Sure it had a distinct name, as named by the Romans. The Roman province of Britannia.
The native Britons would not have had a single name for what the Romans conquered, because it was individual kingdoms.
The name of that island in English is Ireland. The fact that the name is also used for the biggest country on it is immaterial.
The English-language name of the nearby island the Romans mostly conquered is Britain. All I’m saying is “use parallel terms that aren’t anachronistic.” Ireland works, because it’s also the name of a geographical feature; England doesn’t.
PS: Britannia is not the same as England, as the Romans conquered Wales and parts of Scotland, as well.
That’s a silly distinction. “England” describes both a state and the geographical area occupied by that state. It’s also worth noting that Roman England very closely tracks the modern state plus Wales.
Here’s an article on Roman contact with Ireland. Roman writers had some knowledge of the island & Roman artifacts have been found. The possibility of an invasion has been suggested but Roman trading stations are more probable.
Maybe, but I don’t see why you’d prefer the less accurate “England” to the more accurate “Britain.” Unlike the Romans, though, I concede defeat quickly: do what you like.
History nitpick: The withdrawal of the Roman forces from Britain, in/around 407, was basically a matter of prioritization. It happened immediately following, and as a direct response to, the “Crossing of the Rhine” in 405 or 406. That is, the invasion/migration of an absolute metric boatload of barbarians, from a number of tribes and confederations, into Gaul.
But yes, that decision was a made by a rogue general who declared himself emperor in opposition to Honorius, and who was later indeed recognized as co-emperor for a time (before coming to a sticky end): Constantine III.
(As for the ongoing anachronism nitpick: I hadn’t really thought about it, but I guess “Britain” is the term I always hear used for the bit of the island that the Romans occupied. Which of course is Latin for “the weather sucks, the food is awful, and I want to go back to Italy”. 
)
Well, I’m not about to invade England/Britain, so that’s fair enough.
What exactly would they have found in Ireland. More rebellious half civilised tribe? Rain by the metric tonne? Even more locals taking potshots at them?
They had all that there in Britannia.
And from the source:
That’s as conclusive as you can get.
Agricola never mapped Ireland, so it means nothing for him to say he could have conquered and held it. It’s like Columbus saying he could annex the Americas for Spain based on his exploration of Hispaniola.
Agricola almost conquered Scotland. And yes, he was apparently of the opinion (rightly or wrongly) that Ireland could have been taken and held with little effort.
The British Isles is a bit of an odd case in Roman imperial history. The fact that there’s a wall right across the middle of an island illustrates that. I mean, why not finish the job? It looks like it should take about five minutes. You’ve basically conquered the known world. So why does that corner of the map look so screwy?
I don’t have a proper answer, but I think that maybe it’s an illustration of an often ignored fact about Roman expansion: There never was a master plan. The Roman Empire may look like something designed, with natural borders on the Rhine and the Danube, the desert in Africa, and… well, OK, more of a half-assed and heavily militarized state of affairs on the eastern frontier. So there’s that, too. 
But it was actually more an empire constructed by way of a great big tangle of individual short-term decisions, made over the course of centuries, and reflecting varying and sometimes conflicting policies. In a sense, it came about as much by accident as by design.
And, basically, no one ever made the decision to finish up Scotland or conquer Ireland. For various reasons, it never made it to the top of anyone’s priority list at any particular time. Is a couple of foggy islands hanging off the edge of the world, inhabited by tattooed lunatics, really what you want to spend even more legions on during this or that particular time in history? At the end the day, the cost-benefit analysis never landed on the side of “yes”. Or at least it didn’t for a long enough time at a time.
Maybe it’s like the way you can have a nice house, with a neatly kept lawn, but there’s still that crappy shed in the back yard, that you can never get around to cleaning up. You never made a master plan that went: “Right, that shed stays a mess, for reasons X, Y and Z”. It’s more that it’s always just too much short-term hassle and too little gain to get around to it. Because, well, is that what you want spend time and money on this month?
If you read the accounts as propaganda rather than straight history (in other words, assume that Tacitus is spinning Agricola’s accomplishments rather heavily, and likewise other writers), it seems clearer that the Romans were fine at conquering flatland when they had good supply lines. It’s not at all clear how effectively conquered the mountainous areas were in Wales. Scotland’s mountains are higher, its mountainous territory larger, and the climate less forgiving. One possible reason that the Romans didn’t conquer Ireland was that they were too focused on conquering the northern part of Britain. Ireland certainly would have been easier to conquer than the lands north of the Wall.
Again, look at later history: the Normans conquered Ireland, more or less; they had to intermarry into the Scottish royal family and Normanize the royal culture from within.
It’s also worth noting that Ireland wasn’t really worth conquering. For the most part, its soil is too rocky to be valuable arable land. That’s a big reason why potatoes took off there in such a big way: it’s a bad place to grow wheat and other cereal staples.