  The Jesuit missions in South America were an important and unique advance in
Christian evangelisation on the continent until the expulsion of the Order in
1767. Although the history and cultural aspects of these missions and their
most iconic buildings have been extensively studied, the archaeoastronomy of
the Guaran\'i peoples of the Province of Paraquaria (Province of Paraguay) has
only been recently considered, with the existing studies focusing primarily on
the orientation of their churches. The paper presented here, which is the first
archaeoastronomical study of the Jesuit missions of Chiquitos in eastern
Bolivia, is an attempt to continue and complement the previous
archaeoastronomical studies of the region. The methodologies employed involved
the analysis of the Jesuit churches that currently exist in this region,
namely, the on-site measurements of the orientations of eight churches
currently standing and the ruins of a ninth church of which only a
free-standing bell tower and parts of the side walls remain preserved. The
orientation measurements of a tenth church, which we were unable to visit, were
determined via the use of satellite maps. The landscape surrounding these
churches was then examined in detail and furthermore, a detailed cultural and
historical study of the characteristics of the villages where the churches are
located was carried out. Our results show that, unlike the churches of the
Province of Paraquaria where meridian orientations in the north-south direction
stand out, half of the studied churches have shown potential canonical
orientations that seem to be aligned to solar phenomena, with three exhibiting
precise equinoctial orientation. We propose reasons for these orientations,
including the possible relevance of illumination effects on significant
internal elements within the churches - effects that were generally sought in
Baroque church architecture.
