In Classical architecture, a member or part between the capital proper and the shaft of an Order, meaning literally ‘below the neck’ or the ‘lower part of the neck’. Its exact meaning seems to have varied slightly according to the source consulted or the Order used. Vitruvius appears to suggest it refers to the apophyge, but Renaissance commentators on Vitruvius, while accepting the apophyge/apophysis connection, also apply it to the lower part of the capital between the astragal and the echinus, so it meant the frieze-like collarino, gorgerin, or neck of the Tuscan, Roman Doric, and Greek Ionic (Erechtheion) Orders. In the Greek Doric Order it meant the horizontal grooves, reeds, or fillets encircling the column, the part of the column above, with flutes, terminating in the annulets under the echinus being the trachelion(um). However, in certain archaic Greek Doric Orders (e.g. the C6 bc ‘Basilica’ at Paestum) the hollow ‘necklace’ of vertical stylized leaf-like forms is defined as the hypotrachelion(um).
J. Curl (2001);Dinsmoor (1950)