How did the Romans figure out where North was ?

[Malthus]

Obviously it was aliens that imparted this knowledge.

…

[Well, Egyptians and Babylonians were technically speaking ‘aliens’ before their conquest by the Romans … ]

[Mr.Kobayashi]

They used winds as compass directions, what we’d call north they’d call septentrio. On how they found it, they did it by the stars;

Septentrio (N) – Isidore relates it to the Arctic circle (“circle of seven stars”, i.e. the Ursa Minor). Septentrio can mean “commander of the seven”, and the Pole Star is indeed the chief star of the Ursa Minor. An alternative etymology derives it from septem triones (seven plough-oxen), a reference to the seven stars of the Plough (Ursa Major).[75]

The Greeks figured it out first, though.

[njtt]

@Mr.Kobayashi

They used winds as compass directions, what we’d call north they’d call septentrio. On how they found it, they did it by the stars;

The Greeks figured it out first, though.

Your first link says, in its first sentence, that Isidore of Seville, who is the person under discussion there, was not around until centuries after the fall of Rome. So that is irrelevant.

Although it is true that the ancient Greeks did know how to find the compass directions, they did not depend on the winds to do so, and a quick glance at the rest of this thread would have told you that accurate (and non-wind based) methods of finding north were known long before the time of the Greeks.

[Mr.Kobayashi]

@njtt

Your first link says, in its first sentence, that Isidore of Seville, who is the person under discussion there, was not around until centuries after the fall of Rome. So that is irrelevant.

Although it is true that the ancient Greeks did know how to find the compass directions, they did not depend on the winds to do so, and a quick glance at the rest of this thread would have told you that accurate (and non-wind based) methods of finding north were known long before the time of the Greeks.

He was compiling earlier sources, so hardly irrelevant.

They named cardinal directions after winds, not depending on winds to find them. Reading comprehension not a strong point today?

[njtt]

@Mr.Kobayashi

He was compiling earlier sources, so hardly irrelevant.

They named cardinal directions after winds, not depending on winds to find them. Reading comprehension not a strong point today?

I understood perfectly well what you were saying, and could thus see that it was a mixture of the irrelevant (nobody asked about how compass directions were named), the redundant (issues already covered in the thread much more fully), and the misleading.

[Mr.Kobayashi]

@njtt

I understood perfectly well what you were saying, and could thus see that it was a mixture of the irrelevant (nobody asked about how compass directions were named), the redundant (issues already covered in the thread much more fully), and the misleading.

You dismiss a source based on a nanosecond of reading then accuse me of saying something I explicitly did not. In a thread about Roman compass directions it’s clearly irrelevant what they called them. :rolleyes:

[CC]

Would lodestones have been any use to the Romans?

[Grey]

You can find a wealth of information on Roman construction techniques by looking at Virtuvius’ 10 Books on Architecture. Given he died around 15BC it’s should cover the question nicely.

From CHAPTER VI : THE DIRECTIONS OF THE STREETS; WITH REMARKS ON THE WINDS

6. In the middle of the city place a marble amussium, laying it true by the level, or else let the spot be made so true by means of rule and level that no amussium is necessary. In the very centre of that spot set up a bronze gnomon or “shadow tracker” (in Greek σκιαθἡρας). At about the fifth hour in the morning, take the end of the shadow cast by this gnomon, and mark it with a point. Then, opening your compasses to this point which marks the length of the gnomon’s shadow, describe a circle from the centre. In the afternoon watch the shadow of your gnomon as it lengthens, and when it once more touches the circumference of this[27] circle and the shadow in the afternoon is equal in length to that of the morning, mark it with a point.

7. From these two points describe with your compasses intersecting arcs, and through their intersection and the centre let a line be drawn to the circumference of the circle to give us the quarters of south and north. Then, using a sixteenth part of the entire circumference of the circle as a diameter, describe a circle with its centre on the line to the south, at the point where it crosses the circumference, and put points to the right and left on the circumference on the south side, repeating the process on the north side. From the four points thus obtained draw lines intersecting the centre from one side of the circumference to the other. Thus we shall have an eighth part of the circumference set out for Auster and another for Septentrio. The rest of the entire circumference is then to be divided into three equal parts on each side, and thus we have designed a figure equally apportioned among the eight winds. Then let the directions of your streets and alleys be laid down on the lines of division between the quarters of two winds.

[Really_Not_All_That_Bright]

@Freddy_the_Pig

He mentioned “using a compass” only to point out that the Romans didn’t have compasses. So they could not possibly have aligned anything to compass north.

Sure they did. At least, the Greeks had them, so the Romans presumably did.

[Grey]

Well don’t forget a compass doesn’t always mean a North/South directional tool.

[gazpacho]

@Really_Not_All_That_Bright

Sure they did. At least, the Greeks had them, so the Romans presumably did.

Is there evidence that the Greeks and Romans used magnets for compasses?

[Peter_Morris]

@Kobal2

To put it simply : it’s all well and good to say “oh, you just find Polaris, and there you are”. But in order for us to know that Polaris semi-accurately indicates due north, somebody, at some point, had to do all the calculations and observations and verifications and so forth.

Not really. The point is, the constellations rise and set. They all turn about a particular point. Stars far away from that point turn in a great big circle, stars close to that point turn in a tiny circle. Thjat point is north by definition. And that’s something that can be eyeballed easily.

[PlainJain]

Maybe that’s what they used the dodecahedronds for.

[slipster]

Some years ago I read a book on Egyptology which cited another method.

It was said that the ancients would build a “visual horizon”–that is, a low wall which would cut off the sight of objects beyond it. A person seated a small distance behind this wall would direct an assistant to mark the place on the wall where some bright star or another could first be seen as rising up above the wall. Later, the observer, seated in the same exact place as before, would direct an assistant to mark the place of the wall where the star descended out of view. The place on the wall midway between these two points would be measured and marked. A rope would be drawn from this point to the observer’s seat. This line would run north–south.

This astronomical system, done with care, would be more accurate than looking directly to The North Star at a particular moment as the star observed would be describing a circle with true north at its center–just as Polaris does.

[md2000]

@slipster

Some years ago I read a book on Egyptology which cited another method.

It was said that the ancients would build a “visual horizon”–that is, a low wall which would cut off the sight of objects beyond it. A person seated a small distance behind this wall would direct an assistant to mark the place on the wall where some bright star or another could first be seen as rising up above the wall. Later, the observer, seated in the same exact place as before, would direct an assistant to mark the place of the wall where the star descended out of view. The place on the wall midway between these two points would be measured and marked. A rope would be drawn from this point to the observer’s seat. This line would run north–south.

This astronomical system, done with care, would be more accurate than looking directly to The North Star at a particular moment as the star observed would be describing a circle with true north at its center–just as Polaris does.

Yes, L. Sprague de Camp’s The Ancient Engineers IIRC, mentions this technique too. If you have time and a clear sky, marking star-rise and set will give a relatively perfect east-west line. Creating right angles was trivial by then; supposedly the Egyptians knew of the 3-4-5 triangle. For added bonus, use a trough of water to establish level.

the Egyptians were good at this because they had to re-survey fields regularly after the Nile’s annual floods.

[Kobal2]

@PlainJain

Maybe that’s what they used the dodecahedrons for.

Nah, those were used to calculate two-handed axe damage and the hitpoints of barbarians (per Iugaxus, *Manusliber *Ludium III.Ve)

[QUOTE=m2000]
For added bonus, use a trough of water to establish level.
[/QUOTE]

The Romans had a better (and more portable) tool for that called the chorobates…which was pretty much just a portable trough (with added plumb lines for finickier work).
The improvement was that it could also be used to establish definite but very slight and regular inclines. For aqueducts and sewers, you see.