An initial study of long-lived loops observed with TRACE (Lenz et al., 1999
) shows that they have no significant temperature stratification and that t
hey are denser than the classic loop model predicts. Models that agree bett
er with the observations include a loop consisting of a bundle of filaments
at different temperatures and a loop with momentum input by MHD waves. Som
e implications for coronal heating models and mechanisms are discussed.