A free 5-part series on the paritta (protective, safeguard) meditations. Tricycle has a subscription based course in which they describe these meditations in the following way.
From the wide range of meditation subjects found in the Buddha’s discourses, the ancient teachers of the Theravada tradition have selected four subjects and grouped them into a set known as “the four protective meditations”: recollection of the Buddha, the meditation on loving-kindness, contemplating the unattractive nature of the body, and mindfulness of death. The four are called “protective meditations” because each offers protection from a particular unwholesome tendency and reinforces a beneficial quality essential to the path. The four can be developed either as a preparation for a more intensive type of meditation or as independent subjects.
The protective meditations were included in an anthology called the Catubhāṇavārapāḷi (alt/pdf) that was originally made as a handbook for newly ordained monks. Since then, it has also become a “Buddhist bible” in some homes.