diff --git a/cartographer/kalman_filter/pose_tracker.cc b/cartographer/kalman_filter/pose_tracker.cc
index 427af57..27c8fe7 100644
--- a/cartographer/kalman_filter/pose_tracker.cc
+++ b/cartographer/kalman_filter/pose_tracker.cc
@@ -343,19 +343,6 @@ PoseCovariance Embed3D(const Pose2DCovariance& embedded_covariance,
   return covariance;
 }
 
-PoseCovariance PoseCovarianceFromProtoMatrix(
-    const sensor::proto::Matrix& proto_matrix) {
-  PoseCovariance covariance;
-  CHECK_EQ(proto_matrix.rows(), 6);
-  CHECK_EQ(proto_matrix.cols(), 6);
-  for (int i = 0; i < 6; ++i) {
-    for (int j = 0; j < 6; ++j) {
-      covariance(i, j) = proto_matrix.data(i * 6 + j);
-    }
-  }
-  return covariance;
-}
-
 PoseCovariance BuildPoseCovariance(const double translational_variance,
                                    const double rotational_variance) {
   const Eigen::Matrix3d translational =
diff --git a/cartographer/kalman_filter/pose_tracker.h b/cartographer/kalman_filter/pose_tracker.h
index d0bd5f3..c27542a 100644
--- a/cartographer/kalman_filter/pose_tracker.h
+++ b/cartographer/kalman_filter/pose_tracker.h
@@ -57,10 +57,6 @@ PoseCovariance Embed3D(const Pose2DCovariance& embedded_covariance,
 PoseCovariance BuildPoseCovariance(double translational_variance,
                                    double rotational_variance);
 
-// Deserializes the 'proto_matrix' into a PoseCovariance.
-PoseCovariance PoseCovarianceFromProtoMatrix(
-    const sensor::proto::Matrix& proto_matrix);
-
 proto::PoseTrackerOptions CreatePoseTrackerOptions(
     common::LuaParameterDictionary* parameter_dictionary);
 
diff --git a/cartographer/sensor/proto/sensor.proto b/cartographer/sensor/proto/sensor.proto
index 6058ffc..171b001 100644
--- a/cartographer/sensor/proto/sensor.proto
+++ b/cartographer/sensor/proto/sensor.proto
@@ -34,22 +34,6 @@ message CompressedPointCloud {
   repeated int32 point_data = 3 [packed = true];
 }
 
-// Linearized matrix representation in row major format.
-// E.g. the  2x3 matrix:
-//   | 1, 2, 3 |
-//   | 4, 5, 6 |
-// would be represented as
-// {
-//   rows: 2;
-//   cols: 2;
-//   data: [1, 2, 3, 4, 5, 6]
-// }
-message Matrix {
-  optional int32 rows = 1;
-  optional int32 cols = 2;
-  repeated double data = 3;
-}
-
 // Proto representation of ::cartographer::sensor::RangeData
 message RangeData {
   optional transform.proto.Vector3f origin = 1;