Lowest data level since DateX

Hello,

I'm dealing with financial time series.  I'm trying to find out X in this
sentence:
The most recent close is the lowest level since X(date).

Here's an example of what I'm looking for:

library(fBasics)
data(DowJones30)
tail(DowJones30[,1:5],n=10)

I need to come up with a vector that would look like this

AA             AXP          T            ...
2000-12-21     2000-12-20   2000-12-29

i.e. the last date at which the stocks were trading at a lower level than
the most recent closing.

I know it has to do with min/max, pmin/pmax, cummin/cummax or rev(), but I
can't figure it out.

x <- c(1,4,2,6,3)
tail(which(x < tail(x,1)),1)

x <- c(1,4,2,6,.5)
tail(which(x < tail(x,1)),1)