As a finish line marker an obelisk is certainly effective, but they are awfully difficult to move about, and the same objective could likely have been attained with perhaps 0.1% of the effort by just having some sort of flag pole do the job. So, what's the deal with the obelisks?
It all goes back to Augustus. Even casual students of Roman history will recall that he had a falling out with Mark Anthony who fled to Egypt and to the embrace of Cleopatra. This was problematic in both a practical and a symbolic sense. Cleo years earlier had a fling with Julius Caesar that produced a son and possible rival to Augustus. Augustus you may remember was adopted postumously by Caesar, who was his great uncle. A more direct heir with a royal mother could be a problem.
So in addition to the usual brutality of conquest in the ancient world there were some personal issues at stake.
So fine, after conquering Egypt Augustus felt like taking home some tangible trophy. Oh, he could pick something small and portable, as Egypt is just chock a block with good statuary. But no, he chooses this:
24 meters tall without the later base. Yes, Augustus found the most phallic public symbol in the newly conquered province and lopped it off, effectively saying that he had emasculated the opposition. He also had the potential dynastic rival quietly dispatched .
Am I being a little overly dramatic? Perhaps being a little Freudian 18 centuries early? Lets look at some other official imagery of Roman conquest, the series of Judea Capta coins minted to crow about putting down a pesky rebellion in a part of the world that has been in ferment ever since...
Too subtle? Here is another version:
Augustus actually hauled back two obelisks, one for the spina of the Circus Maximus and the other as a sundial in the Campus Martius. Later emperors all wanted to emulate Augustus, so the pilfering went on for centuries. All told there are eight ancient Egyptian obelisks in Rome, about as many as in Egypt proper, and there are also a number of Roman copies of same. More on this here.
Genuine ancient Egyptian obelisks were not all that numerous. There are only 29 or 30 of them, it depends on how you count unfinished specimens. Other sites around the Empire generally had to settle for copies. The final tally of where the authentic Egyptian ones ended up appears to be:
Still in Egypt-9 although it is felt that several more sank on transport down the Nile.
Italy-11, with 8 in Rome. Most set up at the Circuses, others at temples.
Isreal-1, Herod the Great set one up in his Circus
Turkey-1, set up in the Constantinople Circus by Theodosius the Great
There are several smaller ones in museums, three in the UK, one on temporary loan in Poland.
And then there are the three "neo-Imperial" obelisks, set up to echo the greatness of Rome and Augustus.
Modern Imperialism is a little bit nicer. In ancient times the script was something like this:
"We are Rome. We just thrashed you soundly. We are taking that obelisk".
The modern, civilized script ran:
"We are your very powerful friend. We could thrash you soundly any time we felt like it. It would make us happy if you offered us an obelisk. You would like to do that, wouldn't you?"
It probably helped that the Ottoman officials in charge of things in the 1800s were famously susceptable to private financial incentives.
The British were first. In 1819 the local Ottoman governor offered an obelisk to England in recognition of Nelson's victory at the Battle of the Nile. There it sat as nobody could figure out how to move the darned thing.
Meanwhile the French, not happy with being reminded about Lord Nelson, talked the Ottomans into gifting not just one but two obelisks in 1829. It took four years to move one to Paris, with an effort so draining that the engineer in charge refused to touch the second one.
Having perhaps learned a few things from the French effort, the British moved "their" obelisk in 1877, but not without much effort and some loss of life.
Finally those late comers to the world scene, the Americans got interested. Considering New York to be a world class city the equal of London and Paris, a new record for obelisk acquistion was set...from polite wheedling, through baksheesh, to dedication in Central Park in only three years.
As it happens, obelisks do not fare all that well when moved. The London specimen was damaged by German bombing in World War One. The Paris example has suffered several indignities including being covered with a giant pink condom by protesters and being climbed by daredevil tightrope walker Alain "Spider Man" Robert. And the New York obelisk is being eroded by urban pollution so badly that the Egyptian goverment-before being distracted by the revolution-was saying they wanted it back if we were not going to take better care of it!