  We study some aspects of Maldacena's large $N$ correspondence between N=4
superconformal gauge theory on D3-brane and maximal supergravity on AdS_5xS_5
by introducing macroscopic strings as heavy (anti)-quark probes. The
macroscopic strings are semi-infinite Type IIB strings ending on D3-brane
world-volume. We first study deformation and fluctuation of D3-brane when a
macroscopic BPS string is attached. We find that both dynamics and boundary
conditions agree with those for macroscopic string in anti-de Sitter
supergravity. As by-product we clarify how Polchinski's Dirichlet / Neumann
open string boundary conditions arise dynamically. We then study non-BPS
macroscopic string anti-string pair configuration as physical realization of
heavy quark Wilson loop. We obtain quark-antiquark static potential from the
supergravity side and find that the potential exhibits nonanalyticity of
square-root branch cut in `t Hooft coupling parameter. We put forward the
nonanalyticity as prediction for large-N gauge theory at strong `t Hooft
coupling limit. By turning on Ramond-Ramond zero-form potential, we also study
theta-vacuum angle dependence of the static potential. We finally discuss
possible dynamical realization of heavy N-prong string junction and of large-N
loop equation via local electric field and string recoil thereof. Throughout
comparisons of the AdS-CFT correspondence, we find crucial role played by
`geometric duality' between UV and IR scales on directions perpendicular to
D3-brane and parallel ones, explaining how AdS5 spacetime geometry emerges out
of four-dimensional gauge theory at strong coupling.
