  The initial phase of the inspiral process of a binary black-hole system can
be described by perturbation theory. At the third post-Minkowskian order a
two-loop double box graph, known as H-graph, contributes. In this talk we
report how all master integrals of the H-graph with equal masses can be
expressed up to weight four in terms of multiple polylogarithms. We also
discuss techniques for the unequal mass case. The essential complication (and
the focus of the talk) is the occurrence of several square roots.
