Azimuth: an arc from the zenith that cuts the horizon at right-angles.

Berm: in Roman defensive works, a narrow level strip between a wall and an outer ditch.

Castrametation: the choice of site and design for a Roman, or later, military camp or fort.

Circumferentor: a magnetic compass fitted with two vertical sights.

Counterscarp bank: an earthen bank constructed on the outer edge of a defensive ditch.

Cropmarks: the patterns revealed by aerial photography of the differential ripening of crops in arable fields – the plants remain green for longer over buried ditches and pits but parch out over buried walls and other hard features.

Cunette: in fortifications, a drainage channel.

Dividing engine: a machine for the accurate engraving of the scale on a scientific instrument.

Equatorial instrument: a telescope on an equatorial mount which could be used to measure zenith and altitude.

Equatorial mount: a mount for a telescope with an axis of rotation parallel to the Earth’s axis; by rotating the telescope around this polar axis a star can be kept in view.

Geodesy: the measurement of the size and shape of the Earth.

Glacis: a long tapering slope, formed of upcast, on the outer edge of a defensive ditch.

Hillfort: late prehistoric settlement, enclosed by earthworks or walls and often utilising natural defences.

Hypsometry: the measurement of elevation by observing variations in barometric pressure.

Lunar distance: the position of the moon against fixed stars.

Manometer: a closed and calibrated vertical tube, with an open end submerged in water, by which air pressure could be measured.

Meridian: an imaginary line between the Poles, and thus the north–south line in a particular place.

Pyrometer: a device for the precise measurement of the expansion or contraction of metals or other materials when heated or cooled.

Quadrant: an instrument for observing angles through a quarter of a circle, set vertically with a plumbline to measure altitude or zenith distance.

Roman camp: a temporary defended enclosure for an army unit, bounded by a single slight rampart and ditch, often playing-card shaped on plan.

Roman fort: a permanent garrison post, enclosed by walls of timber and turf or of stone, and by external ditches.

Spherical excess: the amount that the interior angles of a spherical triangle exceed 180 degrees.

Spheroid: an approximately spherical body.